Okay, point taken
The pinky idea came from Eugene's post here, viewtopic.php?f=1&t=66559&p=543132&hilit=pinky+hydraulic#p543132
and also the touch control manual which says to fill to within 1/2 inch of the filler hole. It did meet that spec, but, I get it, I'll try to add more! I just went and worked the hydraulics, and then was going to try again with a bit more hy-tran, but the fluid had warmed up so that it expanded and DID come out the filler hole when I opened the plug. I'll try again to add more when it's cooled down...
I'm 99% certain this is where I filled the reservoir to when I filled it up, and so I don't think I'm losing any Hy-tran into the crankcase.
So I'm not entirely out of the woods yet, but I a large portion of my issue came from my not quite understanding how the system worked. I did not realize that hydraulic power increases with engine RPM. I figured that as long as the rockshaft load didn't stall the tractor, the pump was turning and trying to lift it, and any further RPM increase wouldn't change anything. I just overlooked trying to increase the throttle, oops.
I took off my 3-pt and put back the factory lift, and hooked up my scale -- one end to the inner hole in the implement rockshaft, and the other end to something heavy. At full throttle the tractor could lift about 400lbs dead lift. That was the only thing attached to the hydraulics -- I disconnected the universal mounting frame.
This is much less worrisome! But still it seems 400lbs isn't great. My thought is that since it seems hydraulic power increases with engine power, and since I assume my watery oil is allowing some power loss inside the engine, it's completely possible that hydraulics will be back up to a normal range once I change the engine oil. That also makes sense with why hydraulic power decreases slightly after the tractor has been running -- engine oil warms up, thins out, and mixes more with condensation, leading to slightly lower engine power.
Sound reasonable, or anything else I should look at? Are there even any TC issues that can cause hydraulics to work moderately well (other than low fluid)? It seems most troubleshooting has to do with things either working, or not working -- I mean, I could pass the TC troubleshooting test, since that only uses 300lbs.