I fixed the leaky oil cooler return line at my HST filter today and put on new seatbelts.
I got the Kubota o-rings and just drained the mid pto plug (about 2.5-3 gal). Pulled the filter and filter housing in order to get the lines off. Replaced two o-rings on the return line and on the line that goes from the filter to the charge pump? I think that's it. The old o-rings didn't appear to have a problem.
Cleaned everything up and put back with new o-rings. Ran it for awhile and no leaks. Ran it with neutral range and with the GO pedal pushed to run the pump. No leaks. Loaded up the brakes and pump in Medium range for a while. Backed it up and went forward in limited space a bunch of times. Let run some more. No leaks. I will drive it tomorrow in light and when it's not parked in for the night
While I was there I put in the new belts. The clasp/release belt wouldn't grab. I had to replace them in my last one too. Check your belts they might not even work. hah. $20 closeout at seatbeltsplus.com fits perfect.