I just got an 880 (haven't picked it up yet), but had some questions about the fluids in this tractor. The operators manual says that this model takes  4.5 gal of 10w-30 engine oil in the transmission PLUS Oliver 102-082-A additive.  What is this additive? is there a equivalent product on the market today?  Also the gas engine is supposed to use 90 octane gas. Is this really necessary ? Thanks