Don't know Scotty. All I know is neither my lube oil nor my transmission / hydraulic oil never gets black. In fact, with the engine oil when I pull the dipstick I can always 'see through' it. Only diesel engines I know of that turns lube oil black are DDEC diesels because of the amount of blowby carbon they put back in the lube oil.I took it he was saying that black oil would be rear main engine seal, not tranny.
rScotty