Re: outdrive gear oil difference
All the major brand alkylene oxide based synthetic oils are going to have very low water solubility and good adhesion to metal surfaces, one of the primary differences is the additives that keep pH from dropping if a little water gets into the system, and additives to help carry more water if needed than conventional gear oils. many of ius tend to abuse gear lubes in the outdrive almost as bad as we neglect the lube in the differential on our cars (you can change that?).
In addition, consider that the vast majority of outdrives fail because of poor maintenance practices. Since good synthetic oils will stand a lot more abuse, it's a good investment for most of us.
Everybody I know that runs stuff hard swears by either the merc synthetic stuff or Amsoil. for the incremental difference in cost, and considering the cost of a new drive, I'll stick with the more expensive merc stuff...
