Remember not all Timex cases are water proof! So don't take a Mercury in for a swim....
Not sure I would take any of mind for a swim in fact. But, I have dunked many in cleaning solution becuase of caked on "DNA". A few have leaked a bit but none have been damaged.
But, as you stated thier are three areas to check. One is the gasket under the crown, two is the case back ring, three is the crystal. Generally the crystal are the most likely place where water can get in. This is becuase the plastic and shrink over time.
Models such as the TV cases have a rubber ring around the crystal as well.