First, inspect or test to make sure it's not the belt tang with a
problem - try clipping in the passenger side belt in the drivers' side
socket, and vice versa.  Should be long enough.

 If there's a foreign object in the socket you might be able to fish
it out with a straightened out big paperclip.  Or unbolt the socket at
the car body end, unplug the electrical connector for the 'belt
buckled' sensor to the airbags, turn it over and shake well, and see
if the trash falls out.

 If that doesn't fix it, you already have the old socket unbolted,
pop in a new one from the dealer or a wrecking yard.  Colors don't
matter as long as it's the right model.

 Seat belts and sockets are not supposed to be field repairable -
that's one thing that you don't want to fail in an accident.  Buying
used parts is OK as long as you (or the wrecking yard people) inspect
them thoroughly first, there are clear signs if a seatbelt was being
worn during an accident and should not be reused.

    --<< Bruce >>--