Here we go...

so, last winter i sent one of my drives to THE performance merc dealer of my state... no resl reason to send it, besides the fact i ran them for 10 trouble free years, that is on top of previous owner...

they only changed 1-2 seals, plus maybe 1 shim...

since i ran them with 75-90 synthetic oil i thought it was good since i never had any problem... they sent me the drive back with 3 notes on the drive, like
synthetic is a bad oil
never use synthetic in drives
use only mineral oil

they sure know better than i do about that, they fill it with merc racing 85-90

but i dont get why i was warned that much not to use syntethic oil !

whats your take on that? Seems like most hi hi perf boat run synthetic!

I thought the merc racing 85-90 was a synthetic blend??

That is the one they gave me, did i misread maybe?

Are you sure they're not referring to the brand Syntech?
I'm sure they'd know how to spell "synthetic".

I believe the issue with synthetic is the cone clutch, Ive never ran it and my drive guy said no also. The bottle up top ^^^^ is not a synthetic or a blend

sorry my bad
was just shortening the word to synthec
i edited my original first post
to synthetic

so, in what or where do you use the Amsoil synthetic oils and the likes and in what drives ?

There is no part number associated with this link to compare what you have in hand or if that is considered their "Extreme Gear Lube" but straight from the Mercury Racing sight HERE!
Their 85W-90 Extreme is Full Sythentic.

So, I've been considering switching to AmsOil synthetic for my drive lube. Any reason not to?

Thanks. Brad.

Find a different dealer.

Only reason I can think of not to buy it is those annoying people peddling AmsOil on various online fora. There is nothing wrong with the oil.

There are many other synthetic oils not sold in pyramid schemes, though.