Re: Merc 402 propshaft seal
The water pump seals are for keeping water "in" the cooling system, not keeping water "out" of the gearcase. The gearcase has it's own bunch of seals.
There is a couple of seals and an o-ring on the propshaft bearing carrier (immediately behind the prop), there is a couple of seals and o-ring under the waterpump base in the driveshaft bearing carrier (but nothing to do with the waterpump), seals on the shiftshaft as well.
The ONLY way to reseal a lower unit is to remove it and strip it down (about 50% of a complete tear down).
The prop has to come off and the bearing carrier has to come out. Then you can remove the driveshaft carrier cover and get at the seals/o-ring (after the water pump has been removed). Then you can pull the shift shaft cover and get at the seals there.
Milky gear oil is not always something you can entirely correct. If you live in the Northern US or Canada the wild temperature swings we experience between summer and winter cause gear cases to expand and contract and no matter how well they are sealed some water is going to get in.
Generally, I don't worry about "milky" - if some water comes out first when I pull the plug then that's when I will address the problem.
But if you are worried about a seal and not just temperature related "seepage", take your lower unit to a shop for a pressure test. The test will tell you exactly which seal is defective (if any) so you can target your repair....
