They should replace the entire seat cover or at least the upper back portion of the seat. To prevent it from continuing to happen either make or purchase a seat belt retainer from Kappasphere or look at what they are selling and make your own. They are easy to make out of 3/8" or 1/4" carbon steel.
Frank I

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07 Black GXP

Current Mods:
Leather, Suede and Embroidered Interior by JPM
SOLO Performance Mach Exhaust
SOLO High-Flow CAT
Hahn Intercooler
Westers Tune
Fijita Intake
Dashhawk
Beltronic G-Meter
Painted Calipers
Custom Painted Engine Cover, Intercooler Pipes and Fuse Box

Future:
DEI Cry 02 System for air & fuel cooling
Slotted & Drilled Rotors
Wide Body Kit if I can ever find one that I like