I have a 1989 18 ft stingray with a 3.0 liter Mercruiser engine and
Alpha outdrive. I have a leaking seal in the outdrive that is causing
about a cup of water to enter into the foot about every 8 hours or so
of operation. I am going to have all of the seals replaced, but in
the mean time, I have been replacing the oil in the foot after every
trip to the lake (about 4 hours per trip) just to make sure no damage
occurs until the repairs are made. My question is this, I have been
using the foot oil from a local marine dealer that is made for
"marine" applications. It is 80W90 viscosity. Can I use the cheaper
gear oil of the same viscosity from Wal-mart, being as I am changing
it so frequently or will this lack of "detergents" from the
"non-marine" labeled oil cause a problem?

Thanks,

Dave