After installing 4-5 different gear lubes I tried amsoil and never looked back started breaking prop shafts.Solved that problem by making large shafts for the 3s and 4s. Then we would inspect after 100hrs with perfect gears and bearings.The drives also ran 40-50* cooler with amsoil. Im running Torco in one drive and amsoil in the other and will let Randy with Marine Drives make the decision which works the best.
The #3 drives have sold on this site at least three times and have only had a gear ratio change and the owner sold the 1-1 ratio upper gears that were removed. We shall see.
MY vette and Mercedes came from the factory with synthetics installed,,just saying.