I'm sure that I read in one of the early Ford service manuals that they recommended a water soluble grease that will not plug up the cooling system when it washes out. However, as with pretty much every Model A issue, there are passionately held, opposing opinions on this too. The guy who rebuilt my water pump recommended a water proof grease that wouldn't wash out of the bearings in the first place. The vendors, of course, are happy to serve both religions. I think that either approach is OK, as long as the water soluble greasers are religious about making frequent applications, and the water proof greasers are religious about not shooting so much grease in that excess is pushed on through into the coolant. I am in the latter group, but not particularly proud of it; I know of no way to know for sure how much is too much (until my radiator plugs up some day, at which time I'll know I have been using too much water pump grease for all these--hopefully many--years).
Isn't the water proof grease that the marinas sell intended for use either in trailer wheel bearings and such, where any excess goes out onto the ground, or in motors that use flow-through river/lake water for cooling (no radiator to get plugged)?