Was there much corrosion around the ring? I would look at how the ring sits, in must me on a flat and clean surface. Also check that the metal ring is not bent, might be worth going to the dealer and purchasing a new metal ring. finally, the larger the rubber ring the better for your situation. Consider buying all the rubber rings at Rock Auto, compare them, and install the biggest one that will fit.
The only other thing I can thing of is that maybe the metal ring is not being turned all the way to the close position. It often takes a chisel and rubber mallet to get the metal ring fully in place.
2001 Bonneville SSEi, 219,000 miles.
Whats in my driveway:
1998 Chevy S10 4x4 ZR2, 1999 Olds Bravada, 2001 Pontiac Bonneville SSEi, 2007 Ford F-350 regular cab 2WD, 2008 BMW 335i coupe (Wife'* replacement for her Bonneville). The Bonneville is my favorite of all the cars in the driveway.