my gearbox oil has done 100 thousand miles now, and i want to change it.
the procedure in the haynes manual is to remove the diff cover plate to drain the oil. this is a bit of a bonus and another reason for doing it cos i'd like to see if i can inspect the diff for wear.
what's the best oil to put in it afterwards? haynes says SAE 80 EP. i don't know much about gearbox oil, what do the figures mean? does it work on the same scale as engine oil viscocity.... but only at one temperature?
also, i believe there are two types of gearbox oil, might be mineral and synthetic.... but i'm not sure. whats the best to go for?
is there any flushing procedure to perform?
and finally, the new diff cover gasket is a metal job with a rubber seal. should i use gasket sealant on it? or lube it with grease or gear oil?
any help much appreciated