Is the only way water can get in my lower units through the washers of the fill and vent on the lower unit?
And what is the part number for those washers?
No----There are seals on the driveshaft and prop shaft.----And o-rings on housings.----Pressure test your gearcase to find leaks.-----Or just order a complete seal kit and install it.
The drain plug was the place I had most trouble with letting in water.
But like Racerone said lots more places to leak.
It always help if you tell what your working on???
You have to pressurised the LU up to about 10-15 PSI.
Google pressure test lower unit outboard and you will find how to do it.
Best is to use a special tool for it, some tools only can pressurised some can do both pressure test and vaccum test.
If you have a air compressor and a regulator and a gauge that can handle such low pressure you can do it without special tool.
12-19183 3 (blue) for the Quicksilver and 18-2945-9 for Sierra. Looks like they are the same for both motors. I would get extras and change them out every time you change LU lube. Ebay sells them in multi-packs FYI.
