Agree with Sokoloff. Short of the car having been immersed in saltwater for a year, the shifter mechanism should last. There is a lot of very hard steel used and it makes for a precise feel when it is working correctly. Get yourself a Haynes manual and pull the thing out of the tunnel. You may have to replace the bushings (and you can make these yourself out of PVC pipe etc), but you should be able to make it last the life of the car.
Rick
PS - are you sure this is not a hydraulic issue? If your slave cyl isn't throwing far enough you may get the same thing. I think your mechanic is clueless....
...and if that's the only thing wrong with your 240D, I would like to submit an offer
