Yea, but if the spec oil (Mercruiser) doesn't protect their parts what good is the spec?

Mercruiser oil wasn't tested in the article he linked.

Never said Merc didn't meet spec. Just Royal Purple doesn't even meet 75w-90 spec out of the bottle. Neither does the "famous" Lucas. I would use either if it was given to me free.

I too on the advice of Max Machine worx have been running amsoil severe gear mixed with Lucas additive, my lower gear life doubled when I started having my lower gears Cryoed/iso polished (30 hours vs 10-15) and it doubled again (50-60) when I quit running that garbage royal purple and switched to the mix that is mentioned. However,as new products are developed such as this neo you guys are talking about I am not opposed to trying some, Smitty

As far as the original question,running a synthetic motor oil, it is not EP rated that I know of and I do know that GPM tried some in his drive behind 1400 or 1500 hp and the gears lasted about 2 or 3 hours but the set-up work that was done to his drive at the time is questionable, Smitty

First of all why try and fix something that isn't broke. But after comparing the little bit of info they give you on the NEO oil on their website to the AMSOIL Marine Gear Oil, the AMSOIL is just as good, and if I remember correctly, half the price if not less.
http://www.neosyntheticoil.com/gear-oil-75w90rhd/

http://www.amsoil.com/storefront/agm.aspx

And if you're concerned with Flash point numbers, which is about all NEO gives you, if hit those temps, you've got other issues!!!

Not too mention, they say nothing about handling water intrusion.

Well, so far so good with the AMSOIL MCF in Bravo X's. My buddy with a 2011 32 Sunsation with new Merc 502's has put the MCF, motorcycle oil in his drives. We ran about 80 miles today, and the boat ran awesome!

Well, for one thing you aren't looking at the correct product. The marine gear lube isnt' even listed on NeoOil's website. Amsoil is not just as good as Neo drive oil that we designed and we guarantee our oil for 75 to 100 hours depending on application, so by the time you change your amsoil every 8 to 10 hours you have spent more money than buying the NeoOil 75-90MRHD oil.

You better change your buddy's oil because that motorcycle oil does not have the ability to last in a Bravo drive for any length of time.

Really? What makes you say that?