I'm looking to change my lower unit oil on my mid-90s Tohatsu m40c. I looked at the manual and it stated SAE 80w-90 for the gear lube. Do I NEED to get the Tohatsu brand gear lube or am I okay with a Pennzoil Marine SAE 80w-90 API GL-5 gear lube that can be bought at my local store? I've noticed people saying buy the manufacturer lube but does it really matter?