Steve that's interesting about the plug - I have no idea what you're talking about - I don't think mine has one?
Although - what I did find when looking for the plug is a black plastic sleeve that was pushed up against the handle which I hadn't noticed before. It looks suspiciously like something that might help seal water out of shaft/shaft join. I hope this photo shows it (I slid it down the shaft a bit so it's easier to see). Where does it go?
Bnesupgirl - I haven't got the same problem as you, but when my old paddle was getting repaired, I borrowed one that had the same problem as you. There was a chip in the corner of the handle that was slowly letting water in, but then it couldn't get out. The chip was barely noticeable but was definitely the culprit. I drilled it out, let it drain and plugged it with some epoxy.