Well it rained today, on the way to work it started, during my shift I had to drive to another store to pick up some product still raining, then I finished up my shift about 7 hours later. During these 7 hours rain had crept in through my driver side mirror (my windows were rolled completely up all the way)

When I got in the car and started it, and went for the radio I noticed no sound coming from my left side, that's when I noticed several drip marks where the water got in under that shark fin or sail panel. I drove home fast as possible and took the door apart. Pulled the speaker and noticed it was wet but not soaked so I dried it off and put it back in, and it turned right on and sounded as good as it did before. Phew

What I am wondering is, has anyone else had this problem? How'd ya fix it? And, assuming that the speaker doesn't get wet again, will it be fine until it finally dies of old age?

I'd say take it off and reseal it with a thick bead of door moulding adhesive
That might stop it and you could check with a hose to be sure. I would keep the
speaker out till you know your not going to ruin it. I've never heard of
this as a common problem before though

Your door is actually designed to allow water to pass through the inside of the door skin (look on the bottom and you'll see holes to let water run out). The speakers should be okay. I've never had issues with mine and I've had puddles of water on my carpet. IF you are worried though, get some electrical grease. It's meant to keep electrical connections from corroding due to moisture. You can also buy/make a baffle for your speaker that diverts water away. It will take some engineering to make, but that's up to you.