It's THF, not TDF. Good fluid, all I use actually. Rotella Hydraulic fluid ain't bad either and TSC carries that. Hydrostats require hydraulic fluid not gear oil.The GL-4 80 or 90 is gear oil, which you don't use in the HST. It's for the front axle.
I have used Mobilfluid 424 and Duragard semi synthetic HST fluid in my Branson. The Branson dealer is also a Mahindra dealer and when I did my first change, they suggested Mahindra's HST fluid.
I think the 424 is now called Delvac and is available as TSC. I'd also use Chevron TDF 1000 if that is available locally.
Copied and pasted from another thread...Folks,
I've never owned a tractor before, but was a pretty good shade tree machanic in my younger days. I recently retired from the military, bought 20 acres and inherited the tractor with the property. It has 209 hours and I just had the local Deere dealer replace all the filters, but HSTs are a new thing to me. Hydraulic oil looks a bit low and manual says I need API GL-4 #80 or #90 Mahindra Universal tractor fluid, but the closest Mahindra dealer is over an hour's drive the away - is there a hydraulic oil I can get from the local Tractor Supply or Deere dealer that I can use?
Sean