weather strip worn again

i have a 2003 GT conv. the weather strip that protects the rear window keeps wearing away. I have had them replaced twice so far, and need new ones again. It has gotten so bad that it rubbed of the strip on the back window and is starting to chip away at the window. I have the mach 1000, and am not sure if the vibrations are causing it, or that the door isnt latched properly. The dealership said that there was nothing wrong with the lock or door, so, i am still wondering why they wear so quick. Any ideas on what can be done to help them from wearing so quick?

Steven

try a different shop to repair it?