190xt Frost Plug Heater Leaking

I removed the frost plug this morning and have installed the Katz engine block heater, but I can't seem to get a good seal and it continues to leak.  I have torqued it about as much as I can according to the instructions so I don't want to overtighten and break the wing nut.  The O-ring doesn't really fit tight in the hole before I tighten it, so it doesn't surprise me it leaks.  I would think it would need to offer some resistance when I push it on to be a better seal.  Someone recommended using permetex aviation sealant #3 around it, since it doesn't dry hard and it would seal it.  Anyone else run into this problem?  Any recommended sealant or do I buy a larger O-ring?  

It is a pretty significant drip and I haven't even turned on the engine.  The other thing is the frost plug isn't seating perfectly flat.  I have scraped and got everything out of the hole so isn't crud causing it not to seal.  I would lose a lot of fluid as it is right now.

I bought a kats 600 watt 1 1/4 heater from allstates ag. While it doesn't fit perfect, anything smaller or larger would be hard to imagine fitting at all. The o-ring seems to be small. I get a constant drip. Any better product to use?

Plaster the sealant on it but leave the antifreeze level below the plug for a day or so. Give the sealant a little time to take a set. Filler her up and go to work.

Thanks everyone for all of the suggestions.  Let me address some of the statements above.  Yes, that is the model of heater that I purchased.  I am suspecting that the motor casting is possibly creating a problem.
 
1) The casting hole inner lip is actually off center and this made it difficult to insert the heater with the wing on it.  I ended up taking a drill on the high side of the lip and notching it to get the wing to slip behind the lip.  Even though this helped, there is potentially a clearance problem with heater elements.  They are very close to the edge and since the lip is oblong, it may be causing a problem.

2) The reason why I am not totally convinced the oblong lip is causing me the problem is that when I slip the heater into the hole without the wing and push it on, I still get a little "rocking" as I push on the top or the bottom.  It should lay flat no matter where I push.  This indicates to me that the outer casting is not flat or the inner lip is not flat.  I think it is the inner lip that is not flat.

3) I rotated the heater element such that it is not touching anything.  I stuck my finger in there to see what I might be hitting and I discovered that the heater needs to be oriented at a 45 degree angle pointing up and towards the front of the tractor.  This is about the only place it will work.  So, I have tried multiple positions.

4) I do think that I need a thicker O-ring.  If the o-ring was touching on all sides, the heater should stay put when I push it on.  If I let go of the heater before tightening, it droops to the bottom.  So, the O-ring does not have a good seal.  The groove in the heater for the O-ring isn't really large so I have to be careful on just how thick of an O-ring I use.  I have also thought about putting another thin O-ring right up against the flange of the heater to provide a second barrier but this may create a problem when trying to tighten.  Certainly, If I did the second o-ring, I would have to chamfer the opening as the above diagram shows.  I will also say that some of the pictures including the one above shows a thicker O-ring than what I have.  Did someone at the factory have a bad day and put the wrong O-ring on it?

5) My only concern on using a sealant is that it might be tough to remove later if I have to replace the heater.  Using a softer sealant should make it work.  I assume the permetex can handle the high heat generated.

My current plan of attack is to do the following:

A)  I am going to try and take some more of the high side of the oblong inner lip off with my drill.  This might make it seat better.
B) Get a thinker O-ring and see if that stops it from leaking
C)  Use thicker O-ring and some sealant and let is set for a day as suggested above.
D)  If none of this works, then I will uninstall everything and put a frost plug back in.   

I believe Option C will work and provide confidence that it shouldn't leak in the long run.  This also may help resolve the inner lip not being flat as I suspect.

I can't believe how screwed up this simple task has become!  It may be due to the casting hole or it may be due to the wrong O-ring but it shouldn't be this hard.  If anyone sees a better path or something wrong with Option C, please let me know.  I probably won't get to it until next weekend.  The only thing I am not sure about is the sealant type that I should use.

Yes, I did look at the zerostart version today and they might have two advantages from the pictures I saw over the kats version. Looks like the heating element is oriented in the center rather than the side, which would help me due to oblong issue of the core plug lip opening, and the screw to tighten the wings looks to be a little more stout. At this stage, what's another $40 if it works right. I am going to try the O-ring first and then decide. Thanks for the idea.

Steve, sometimes them simple complecations come from those who sell you the "These will fit with no problem" items... or the manufactor of them didn't do their home work first.

I tried to do my homework, but my early 190XT required a jump of faith.  The Katz block heater I selected isn't actually listed as working for a 190XT because they list the model  that uses the two bolts to attach it for the 190xt.  They ignored the early 190xts like mine.  Had a owned a late model 190xt, that would have been done in a matter of minutes.  The Zerostart catalog lists only the 175 as a model that it was designed for, but it should work in my case too.  I have a 1 1/4 opening and so either of these models should work, but they aren't listed as working.  My choice was to try it or use a Tank heater.

The casting process for these core holes isn't high tolerance, so it not fitting perfect isn't surprising.  The offset core hole that I encountered and had to deal with in my block may not be common either, but that core hole wasn't meant for a high tolerance part or block heater when it was designed.  My inexperience in doing this job doesn't help either.

I will conquer this one way or another, and be thankful if you have one of those bolt on models.  I have new O-rings coming and some sealant.  I will report back this weekend on my now 8 hour and counting adventure to install a block heater in my older 190xt!

I know this topic isn't very interesting because I might be the only guy in the world to have to spend an entire weekend installing a block heater.  Just in case there is another unlucky fool out there like me, I have documented the trail.

Calico, many times we (forum members) spend many hours reading and advising and some of the info is free... and you know what they say about free, it's worth what you pay for... but, often times when the people that needed help get their problem fixed, they forget to come back and tell us what the problem(s) really were and how they got it fixed.
  Whats that Red and Green line...? "Remember, we're pulling for you. We're all in this together."  mmm fox worthy? "git 'er done"