I think you're not due for a hydro fluid change until 400 hours. I can almost guarantee the issues you're getting are the result of the aeration. I'm not a hydraulics expert, but I'm fairly certain aeration is causing your (and my) issues. We know air compresses whereas hydraulic fluid does not. If you have air in your hydraulics, stuff doesn't work right. Loss of steering is common, as the steering cylinder fills up with air and compresses when you try to turn the wheel. I imagine it does the same thing in the HST (forward/reverse) and MLS (controls the three point). Bottom line, you MUST have fluid in a hydro system for it to do what it's supposed to do. Air is bad for multiple reasons.
Aeration is caused by a handful of things...all of which I researched when my tractor started acting funny. You have suction leaks, cavitation, pseudo-cavitation, and something I forget the name of, but is caused by the fluid falling from the return into the reservoir and causing bubbles (like filling a swimming pool with a hose held above the water surface).
I thought mine was caused by a suction leak, but we've changed just about everything on the suction side we can think of except for the metal tubing. That's every o-ring, the filter housing, filter, clamps on the plastic tubing that joins the front and back tubing, and the tubing itself. We recently changed the hydro pump with the same results. Tractor still acts the same, which is just like yours.
I'm at a loss as to what the issue may be, but I'm going to switch to a premium fluid next and see what it does.
