I'm sure the dealer can fix the leak(*) for you, but I did it myself. I removed the weatherstrip seal around each of the 4 doors, applied clear silicone RTV sealant on the metal edge, then carefully reinstalled each seal and made sure that it was pressed-on as far as it could go. The junction of each seal then had a gap (because each seal had shrunk in length), and I installed each one so the gap was in the middle of the bottom edge and filled the gap with silicone and covered the gap with a piece of rubber tape. After it set up for a little while, I applied a small amount of sealant to the outer perimeter of each entire installed weatherstrip. It took several hours, but it was successful and should never have to be done again.
It'* too bad the seals weren't bonded to the door openings at the factory - that would have prevented them from shrinking and causing the leaks in the first place.
'99 Bonneville SLE, white, 112,000 miles
'02 Park Avenue Ultra, white diamond pearl, 88,000 miles