If you do notice the presence of water in your gearcase oil, there are several options. If you moor your boat and the part of the leg with the drain plug stays submerged when docked, then you should get it pressure checked soon. If on the other hand you trailer your boat each time you go out, or the leg is completely out of the water when docked and there is only a small amount of water in the oil (not milky white) then you may be able to put it off until the end of the season, when the shops are not so busy if you are prepared to change the leg oil a couple of times during the season. Pressure checking will involve removing the leg, propeller and water pump housing. It is possible to do it at home if you have access to a compressor, or even a byycle pump.