2003 L120 with 675 hours and the hydrostatic is acting up again. I replaced it with a new one at about 350 hours and now this one is acting up. The axle broke away from the frame last time mowing last year and now just getting around to looking at it. When the frame broke the drive belt came off and ruined the cooling fan. They say it is not a serviceable unit, it doesn’t have a drain plug for the hydrostatic so I had to turn it upside down to get the oil out and was surprised the oil didn’t look real bad to me but I’m not an expert in that. Can’t find anything that Deere says what type of oil other than their hygard but on other sites I’ve seen where guys recommend replacing it with full synthetic 5w 50. Any of you ever replaced the oil in these? The problem it was having is it barely moves in reverse after it has ran awhile and some have said changing the oil helps this.

The older ones used to use low viscosity hygard, not regular hygard.

Mine leaks it. Hy-Gard TY22000

I flipped the hydrostat, drained the old oil, and refilled with fresh Hygard-and it helped my reverse speed. You can also try a full‑synthetic 5W‑50 if you like. Just pump the control lever back and forth a few times to bleed out any air, grease the linkages, and you should see an improvement.