DEAR CAR TALK: How can I stop rainwater from getting on the floor behind the front passenger seat of a 2009 Lincoln Town Car?

No other place gets wet. Actually, once I found that some water had seeped into the front seat floor after a two-day rainfall, but I think it was overflow from the back seat area. – Margo

RAY: There are three prime suspects in your case, Margo.

One is the two-liter bottle of Evian water that you left under the seat three years ago. But, if we eliminate that possibility, the prime suspect is a clogged moon roof drain.

In order to delay moon roofs from leaking (they all leak eventually) manufacturers create water channels around the moon roof. Those channels usually have four drains, one in each corner. Those drains are attached to tubes that run down inside the roof pillars and drain underneath the car.

Over time, one of several things can happen to screw up this wonderful feat of engineering. Twigs, leaves and squirrel droppings can clog up the drains. The water has nowhere to go but into the headliner and then into the passenger compartment of the car.

The other thing we’ve seen is that the tube can become disconnected and actually separate from the drain. In that case, the water does the same thing and obeys gravity.

So, I’d ask your mechanic to check your moon roof drains. He’ll test them and see if water is draining properly. If not, he can try to gently blow them out with compressed air, which may fix the problem.

If your moon roof drains are all working perfectly (which they’re probably not), the next suspect would be the rubber seals around the rear passenger door. If part of the seal that’s designed to keep water, wind and noise out got torn or damaged, that could allow water to seep in around that door and get on the floor back there.

It’s going to be one of those two things, Margo, so get them checked out. Then you can write back to us and ask us how to get a horrific smell out of a 2009 Lincoln Town Car that had a long-term water leak.

Got a question about cars? Email Car Talk’s Ray Magliozzi by visiting the Car Talk website, www.cartalk.com.