OK. Found a picture. The keyword turned out to be: STRAINER FILTER for JD5205.
Courtesy of Weingartz.com who has a terrific JD parts site.
Sure enough, it looks just as expected. Early strainers were stainless screen on a stainless frame, now plastic screen on a nylon frame. I guess that's either called
"high tech" or "progress" in tractor adv.-speak.
If I'm reading the transmission casting illus. correctly, your strainer access is down low & just forward of the left hand rear axle.
You can see how the strainer slides in. If all is right, it should move easily.
What is not shown in this illustration is that far end is a pretty tight fit into a locating hole in the transmission case casting. The designer doesn't want to give more than 0.003" clearance, because that's the size particle it is supposed to filter.
Because of that tight fit, a problem can happen if crud is in that blind locating hole, and/or the mechanic misses getting it completely down into that locating hole. If the filter is not completely inserted, when he tightens down the mounting screws (#4) the tube is squashed out of shape. The mechanic knows something isn't right, but it is apparently working and not leaking so he leaves it. Actually he knows more than that, but I'll leave that for now. But YOU know what happened when you go to pull the darn thing out and it doesn't want to slide out. Or comes only part way.
NOTE THAT THIS MAY NOT BE YOUR STEERING PROBLEM.
But anytime that hydraulic symptoms include any symptom that could be due to low flow, you always start with the cleanable strainer and work forward.
The next thing after getting the cleanable strainer right is to make sure you do not have any suction leaks, flattened pipe, or saturated spin on filter between where I've written "oil tube should fit into this hole, and the input to the hydraulic pump up on the engine.
Only after we have this suction side fluid feed system to the hydraulic pump all in good shape do we go after seals in the hydrostatic steering assembly.
rScotty