What makes you think you have a liquid lock? If you have sea water dripping on the starter and it got PROGRESSIVELY harder to start you might just have corrosion on the starter/solenoid connections. This is very easy to diagnose. First, look at the connections. Do they look corroded?
Take a multimeter and test your voltage at the battery posts. Hopefully it is 12.8V. Then test it on the two posts of the solenoid. Is it 12.2? That would make the engine start sluggishly.
To fix take off and clean the connections. Oh and fix the saltwater leak. I would recommend removing the battery cables at the battery first though as I once touched both poles of the solenoid with a metal wrench. It instantly arc-welded the wrench to the posts and began starting the engine. Scared the %%$$!!! out of me!
You also may have corrosion in the starter. I once submerged my yanmar starter in sea water (don't ask) and it was pretty straight forward to "carefully" pull it apart, clean it and put it back together using the exploded diagram from the yanmar manual.
Hope this helps.
MedSailor