I have a 1991 300d, does the same thing. Be careful, because they have pyro stuff in the seat belt to stick in place during a crash.

You can take your stuff around it off, which is pretty easy to do, then use an air blower to blow all the lint off from years of rubbing along your clothes when it retracts, then once it's blown off, suck it up with a vacuum cleaner. This might help, but will not cure the problem.

Jeff