This is a well designed pump. The oil seal is isolated by a weep slot or hole from the water side of the pumps and seal. Even if the water seal were to leak the water will just drain out the weep hole. If the oil side weeps it too will simply drain out the weep hole. Neither side of this pump can pressurize or leak into one another.
On occasion I have seen weep holes plugged with dried salt. In theory this could create some pressure that could press though a weak oil seal when the engine was of and the seacock open. With the engine running the crankcase becomes pressurized and should reject the water. I have yet to see any water in engine oil even with a salt encrusted weep hole. It is quite possible that if water did get in, it was so minimal it was evaporated off with engine heat. Either way if you have dried salt, water leaking or oil leaking you'll need to rebuild the pump.
Unfortunately some pumps, by certain makers, do not have or utilize adequate weep holes so a water side leak could inevitably leak into the engines oil or vice versa.