Auto body repair & detailing: Water leaking into interior, Ford F150, body seams, speedometer cable

Question
Hi. I am preparing to buy a 1996 Ford F150 XLT. It's in pretty good shape except there is water on/in the carpet on the driver's side against the door. The seller says he thinks it is the door seal. He has determined it is not the windshield. He has not been in the car when it is leaking and says he only notices it after a heavy rain. How does one replace the door seal and do you have any other thoughts about what it may be? Are there drain holes or similar which could be blocked? Thanks.

Answer
This is not a problem of drain holes. Water leaks are really the realm of the professional repair technician, because they can have so many origins. How does the owner know it isn't the wind screen? Is he a professional body tech? I doubt it. If it's a door weather seal, the leak will always be accompanied by wind noise. Cracks in calking between body seams can cause leaks, a rubber seal around the speedometer cable can cause leaks, where the door wire harness goes into the body can cause leaks, the stationary glass can leak- you need professional help. If anything, have the owner deduct a few hundred bucks off the purchase price to cover the cost of repairs, or take it to a body shop for an estimate. Water leaks can sometimes be a real pain to track down. Bill