The driver side seat belt holder of a Mercedes clk 500 seat belt is supposed to come forward so one can handle it. Mine has stopped working. Does anyone know how this may be rectified?

Believe it or not, this is a common problem. I have the exact same problem with the same car. Mine was sticking closed. I was able to free it by pulling on it. By the way, the same thing happened to the extendable cup holder in the dash. It got stuck open. I lubricated it with silicon spray and it was fixed. Shine a light into the seat belt retractor hole and look for the place where it moves out to lubricate with an extender tube to the silicone spray.