Differential fluid Question????

[oceantech84]

I've searched around forum,reddit and Google but I would love to hear some opinions on here for a 23' 501a

I have in my garage a 5 gallon bucket of Royal Purple 80w90 max gear. I know the book calls for 75w85 but would like some opinions if I should go for the swap or stick with the book. I also had a hard time finding if I need friction modifier or not.

Thank yall for any help.

 

[Badgertits]

I think I put Amsoil 75w90 in mine, works fine, the front diff I went w/ factory fluid it’s also very hard to swap so had dealer do, you’d be fine w/ that gear oil