I did the pump on my wife's 91 300 CE this past winter...the right metric allen wrench, heat, PB Blaster and a great deal of patience and mine finally came off. I cannot believe that an experienced mechanic was unable to remove it...I agree with one of the previous posts...find a new mechanic as a great deal of time is required in getting to the pump...now you will have to pay someone else to tear it all down again to replace the pump you wanted replaced in the first place.

Antonino