D-19 Hydraulic pump guidence/parts needed

Took a look inside my '62 D-19 # 3948, hydraulic pump yesterday. Reasons for doing so include continuous noise, slow movement, jerky action, bleed down and inability to fully lift  a 1700 # hay bale.
Much to my surprise the cam lobes and cam follower rollers look good. The cam follower to pump measurements were all closer to 2 1/16th" versus 2 1/8th". Don't know if that is too bad or not. One plunger does have some minor marring on top. The fuid was very milky when drained. These seems to be included in the rebuild kit ($152).
What I found in the pump was one 3/4" plunger was missing the washer on the bottom. I haven't found it yet but it must be in there somewhere! Two Relief Valve springs were half again longer than the other two.  Don't know what either indicates as far as pump operation. The intake screen also seems to be coming apart and I found two short pieces of this.
AGCO has the repair kit which I think include the plungers, balls, springs, washers, etc. It dos not include the screen, 3/4" plunger or bottom gasket.
Here are my questions I need guidance with from those more experienced than I (almost everyone!) .
1. Would anything or everything I found cause the symptoms described or is it in the Control Valve assemble?
2. Does anyone have a good, used 3/4" plunger , intake screen (or should I make one out of window screen wire?) and/or bottom gasket for sale (I could make this as well)?
3. How can I get the valve seats out or, should I take it into a hydraulic shop for removal and installation of new seats? No one at my AGCO shop is old enough to have worked on one and they tell me they don't have a "screw type puller".
Any and all help with this will be GREATLY appreciated!!

Thanks Mack! What about the damaged plunger insert? Should it be replaced and if so, where can I find one or three? The flat bottom portion of the other two inserts are quite sharp around the edges. How thick should the collar be?
Are the springs available separate from the complete kit?

Call a tractor salvage yard, they should have the plinger and the Agco dealer should have the other parts.  MACK

I'll get a photo of the insert today. I'm wondering about the wisdom of replacing only one plunger which is scored on the top or, should all three be placed at once? Also do used plunger wear so they won't fit correctly in the block? Would new be advisable? 

I would replace all of them.  MACK