I bought a Kubota B6100 from a buddy. So far it needs battery , new front tires and wheels and a new clutch. I'm going to start with a fluid change the rear end got a little water in the fluid and the engine oil probably well over time for a oil change.
Decent sounding engine, but notice a bit of blow-by coming out the breather tube. Rings may be tight, so maybe try some Seafoam in the oil to loosen things up a bit. Those older engines do usually smoke a bit, but will run forever it seems. Gear oil sure doesn't sound right for hydraulic systems! I think I'd go with 20/50 motor oil for the hydraulic/trans oil, but when changing rear oil, be sure to clean the screen with is below footboard on right side. Screen is on end of banjo bolt going through the suction line going to pump. Screen is bound to be gunked up.
Oh my, with a buddy who neglects a machine like that, he should of just given it to yah!
Well, this will be a nice rebuild blog. Hope to see more action here as progress is made.
I would 2nd the Seafoam or B-12. Bet the rings are dried oil in the weep slots. In some machines that get water down the exhaust pipe to the pistons and rings, pouring in the cleaners would help loosen it all up. Then one must slooooowly by hand crank the engine. Sometimes splitting the machine helps to do this.
As for oil, these Japan tractors are built in the days of METRIC and to the JIS specifications. Thus, the 10W30 diesel or the SAE30 are the norm for these Japan machines. The American old Iron machines need the 15W40. Don't let these small diesels suffer with that thick oil.