Hello all,
I am trying to figure out what's the best thing to replace my trans/hydraulic oil with on my 40+ year old kubota. Manual simply states SAE 80 and previous fluid looked like engine oil. I've been scratching my head at tractorbynet and someone mentioned bob so here I am.
There's basically 2 schools of thought - SAE80W-90, or tractor THF. What say you?

What model Kubota?

M4500DT
Diesel 6cyl gear driven

I would call a dealer and see what they recommend.

Dealers don't really deal with 40+ year old tractors

Original fluid spec has been superseded, and THF (please get a quality product, not some low-priced garbage) is the updated recommendation for shared gear drive/hydraulic systems on M4500.

Two, five-gallon pails will get it done.

So regular old tractor supply THF instead of 80w-90?

It sure is hard to find info on old M4500 tractors, is there a good source you're pulling from?

Get one of the heavier THF and run it in the hydraulic system. Get some heavy gear oil for the front axle if its separate.

If you're going to Tractor Supply, I'd get Rotella HD Tractor Fluid ($49.99/5gal).

Awesome! Thanks ramblejam

Gear driven, but with a hydraulic system. (3 point hitch, loader, or belly mower)

Would this be 2 different fluids?

Hydrostatics on the other hand would be shared.

No, they all seem to use the same fluid for the trans and hydraulics, even the gear drive ones.

Not sure what you're asking, but yes this is not hydrostatic, it's gear driven and apparently the transmission is lubricated by the shared hydraulic fluid.

I would check with the local dealer to be certain.

I was in there today asking about a used G series snowblower they had on the lot. I normally check out the selection of oil and they had quarts of Kubota 80w90 on the shelf. Granted, this could be for PTO boxes too.

I would confirm this with your dealer.

"Apparently" doesn't sound reassuring.