HD5 needs some help

You talk about piston leaking you have to removed the the bolts on head cylinder and pull the head and you should see the packing seal easy to change and about the u-joint you need to removed the 2 rear u-bolt and push the drive shaft in front to clear the rear yoke and pull out the drive for change the joint and about the shifter lever removed the bolts from guide shift lever and the 2 bolt from the housing shift lever and pull out the shaft pivot assambly for checking the trouble and oil hydrolic is 32 or 46 oil and transmission and final drive 80/90 oil

Pull the 2 bolts on side of shift tower - then lift lever up and out - (shift to neutral before pulling) You will find a yoke on lever with a round bushing and a pin through it - the bushing wears as does the pin - easy to make new bushing and increase size of pin if holes in yoke are worn - I increased pin size - then ground 2 flat spots in pin so bolts that go into bushings would hold it secure . I made up new bolts and turned ends to index into bushing deep enough to contact pin - then I shimmed bolts at housing to keep pin in place and have right tension on pin and yoke . 
 On the end of the yoke is the ball end that fits into shifting rails - if it is worn it needs to be built up so it doesn't slide between shifting rails (both in width and to make rounded end)

A view of the end of the cylinder and the gland on the cylinder would help . 
On tractomotive loader they used a V ring packing and a packing gland to tension packing - it is a brass gland held in place with 2, 1/2" bolts - this packing can be tightened down and also a ring can be added easily by splitting a packing ring at a bias angle and installing without removing rod from cylinder .

I'll snap a pic of it as soon as I can. It does have two bolts that take a 3/4 box and you can tighten them down. That's basically what my dad did for the last 50 years but when you get them to where it does not leak it creates too much drag on the piston causing the blade to hang up on one side. There is also a long scratch in that particular piston that has been there forever which probably has caused the leak. It's not too deep but I always thought it should have been replaced decades ago. 

Is there a better hydraulic oil that will not hurt anything but maybe thicken up things a bit and cut down on the leaking valve? Would it be the medium or aw32/64?

Got it, I would agree if it has to carry that far the 00 semi fluid wouldn't do that. Not sure why that is all they used..guess they liked repairing those old ACs back then. My grandfathers business had all AC's from 5's to 41's in the 70's. Not sure why the old time mechanic told me that. 

I have the same machine with the same blade. As far as the valve goes, it is easy to fix. First mark the round bushing that the blade control bolts to in regards to the shaft. If you get the orientation backwards the pin may not go back in. The valve has a detent to keep it centered and keep it in float. That makes it a litttle hard to remove the pin, i do not take out the detent as it holds the spool of the valve in place when you disassemlbe it. You can remove if you want iti is the big bolt on the side, it has a spring under it. Remove the pin and round bushing on top. Next remove the square cap on top next to the control. Under it there will be a large threaded rod with a screwdriver slot in it. Remove this but be sure to count the total number of rotations it takes to take it all the way out. Mine was 18. It will be hard at first as it is the releif valve and it has a spring under it. It will get easy and the spring will not jump out. Next remove the six bolts holding the cover on and remove the cover. Therre will either be a seal or oring that seals the shaft. Replace it. Make a gasket with good gasket paper and a ball peen hammer. The original gasket is thin, use as thin of paper as possible as the faces of the valve and cover are machined flat and dont need alot of gasket paper. Clen the shaft. Reassemble in reverse order setting the relief valve back to original. The pin can be a bugger to reinstall, now you can rmove the detent on the side to make it easier. Be sure not to turn the shaft around as it will not work correctly. The seal or oring area does not see full system pressure as this is on the return side of the valve. Dont be scared to tackle this, once you see how it comes apart it is easy to repair. Baker blade manuals are available online. When i get home this weeekend i will see if i can find a pic.