I've always used and had great luck with the Mercury High Performance gear lube. I run it in both my Bravo and my Sportmaster on the little boat. Just did the gear lube in the bravo about 2 months ago after 15-20 hours and it was a green as it was when it went in.
Also, for anyone that uses the Merc lube, go to Walmart to buy. They carry the Quicksilver HP (same stuff) and it's only $9.95 a quart compared to $16.00 at the dealer.