I read your old thread and am inspired to try your "fix" on my loader. Same as your tractor, when it gets warmed up it is a pig. It is worse in reverse than forward but not good either way. I have two theories, maybe three or four that are embedded in these thoughts:
1. I have replaced the relief valves, they were worn badly and visibly washed out.
2. No idea how old the oil is or what the original viscosity is.
3. The machine is a German made Schaeff with a Rexroth hydrostatic transmission. The specs call for 30 wt / ISO 100 hydraulic oil. That is an uncommon hydraulic oil and so it is easy for someone to put the wrong oil in the machine sometime in its life which is about 6,700 hours. Old but not dead, certainly not the little Perkins Parma engine and the Rexroth should have lasted for up to 10,000 hours but may have been damaged a long time ago by contamination. The pump or motor may be just worn out, most likely.
4. Oil wears out as well and I have no idea how old this oil is or what the viscosity is, probably less than half of what it should be.
5. Reverse being worse than forward indicates more wear or some damage on that side of the kidney plate, OK for suck but not so much for blow.
I am going to find some ISO 100 or better hydraulic oil and give it a go.
Thanks for the inspiration to try what I have been thinking about for so long. I'll let you know how it turns out if you are still around.
My little Komatsu excavator requires 30 wt engine oil for the hydraulics but they are just gear pumps.
My Dozer wants AW46 and it is Sundstrand hydrostatic. I can get that at the ag supply store.
ISO 100 is a little hard to come by in hydraulic oil so instead of just engine oil I'll go to the jobber and see if I can get 15 gallons of the stuff. anxious to try this since I use the machine with my brush cutter and need to trim fences this winter.