I have a 10-year-old Miata. After about eight years, the gasket around the driver's side door began to leak when it rained. Annoying, but not fatal. Recently I've noticed a slightly musty smell when I get into the car in the morning. So what to do? Rather than fixing the gasket (which requires replacing the roof as far as I can tell), I took a dehumidifier that I borrowed from Mike Zintel (the PUM of the .NET Compact Framework) and set it up in the car to suck as much moisture out of the car as possible. Once that's done, I'll go through the car with some mold-killing substance (probably bleach) and clean. Then I'll put some silicone sealant around the gasket to see if I can staunch the source of the water. Here's to keeping our fingers crossed.