Is this for a diff or transmission?
I'd recommend (and I'm not someone who drops names often) ordering some Amsoil gear lube from our site sponsors.
I've used a few brands and found a WORLD of difference (for manual transmissions) between oils.
Its something you leave in for many miles. I've had a top major name brand gear oil be spent within 40k miles and the Amsoil I've got so far 80k on it and all is like new.
Give us more info and maybe we can suggest something.
Bill
I have a 2008 Tacoma 4 cylinder 4x4 with manual transmition. It only has about 16,000 miles on it right now, but I was thinking about changing the front and rear differential, transer gearbox and manual transmition soon. the maintenance schedule calls out replacing them at 30K if you are not towing anything, but at 15K if you are. was hoping changing all of them specially with a synthetic gear oil would make it run smooter and quieter. what do you guys think?