If you are talking about the little screen that goes from the fitting into the top of the rock shaft housing I believe JD did a TSB on that and recommended leaving it out and installing the upgrade kit which has the typical canister filter above the top link on the 3 point. They ended up finding out the screen was blowing out and causing debris to get caught in the rock shaft control valve. Your tractor might already have it. Also on the rockshaft control valve you might be able to get away with cleaning it out as best you can and replacing all the o-rings. Blow by the o-rings can be a culprit and is pretty easy to diagnose if there is hydraulic fluid when you removed the cover.
On my 4400 I had the same issues you are talking about minus the broken roll pin. I replaced with New/old stock rock shaft control valve and pressure relief valve and neither of them fixed it. What ended up fixing it was me fine tuning the linkage control rod and the flow control valve under the seat. But I had the same exact issues. Lift up all the way and motor would lug from the pump constantly running until I found the sweet spot in the linkage where it would drift down and hold. The rock shaft control valve is pretty easy to get at so it wouldn't hurt to put new o-rings in and give it a shot before you put out a bunch of green for green parts.
Did your rockshaft lever act as an all or nothing like mine?
Is this correct that there should not be any oil in the cover? I had oil in the cover when I removed it. quite a bit actually. I see what looks like a drain back to the tank, so I assumed it was normal to have oil in there.
As for the filter, it looks like (from what I've been able to search) you need to replace the hydraulic line and the filter is moved up to the straight section. Mine definitely doesn't have that. I may take the line to the local hydraulic shop and see if they can put an inline filter in it. I think I read somewhere that the conversion kit was no longer available, and I'm sure I can probably have it done cheaper locally.
Thanks!
A good video to help make the decision on which Permatex options and decisions.. multiple products. quick cure, anaerobic, etc.
Gasket Maker Overview - Permatex Tech Tip Series - YouTube