1997 Chevy Tahoe Water leak - interior

Interior problem
1997 Chevy Tahoe V8 Four Wheel Drive Automatic

Rear passenger floor behind drivers seat wet. No signs of a leak from the top. Buddy says he bought a new 1997 tahoe and it soon developed the same problem - wet carpet behind drivers seat. Dealer told him they were aware of the defect in the tahoes and repaired it - buddy dosen't remember exactly what casued the leak but thought the dealer says it was coming from the rear fender well? Is this common in this yeaer of tahoes and how can I repair it? Thanks.