I should know by now to leave well enough alone, but I didn't. I have an old JD 165 hydrostatic lawn tractor. Under the seat is a fill tube with a dipstick. I pulled it out and nothing registered on the stick. I decided to drain the rear end and replace the fluid completely. I have come to find out that I don't think I drained what I thought I was draining. Apparently (if I have this right) there is the hydro pump, and the rear end. Separate things. I believe I drained the rear end. What I drained appeared to be 80/90 weight gear oil from the rear end. What the dipstick measures is hydro fluid. I THINK ! AND I MUST STRESS THE "[b:670b92f5e2]I THINK[/b:670b92f5e2]" PART OF THIS. If I am correct, I cannot find where to replace the 80/90 weight gear oil for the rear end. Also, I don't know what kind of fluid to use to top off the hydro oil. Am I wrong on all this? Can anyone help? PLEASE!