Synthetic lower unit lube

[marcortez]

Anyone have any qualms using Royal Purple 75W-90 GL-5 full synthetic lower unit oil in a new F75?

After the breakin period on this motor, I want to change to the RP, as I have lots on hand.

Will, or would Yamaha jack me up on any warranty issues if I don't use their branded lube......either lower unit juice or engine oil?

[boats.net]

Yamaha owners manual recommends to use Hypoid sae#90 gearlube, as long as meets their recommendations.