The seat belts may not properly retract due to an internal fault with the retractor mechanism. Replacement of the seat belt retractor would be required to correct this concern.
Resources for the Repair and Maintenance of your 1999 Mitsubishi 3000GT SL
1999 Mitsubishi 3000GT SL
1999 Mitsubishi 3000GT SL Problems
1999 Mitsubishi 3000GT SL Reviews
Got my car with a blown head gasket for cheap, replaced the engine and did some minor work to it and all in all it does great. Only problem I've had is it seems every year or two Mitsubishi changed the parts on these things, and from one engine (non-turbo) to another (non-turbo) they're like 2 completely different monsters.