Try E.C. European Auto Repair, (817) 292-1449. They are not in the Dallas area but in Ft Worth. They are a tiny family shop that specialize in BMW & Mercedes. I have been using them for 6 years now for repairs that I can't do myself. They are not familiar with performance products, but are EXCELLENT for repairs. They have always done the repairs right the first time.
Also as an FYI - they have no waiting area, so be prepared to have a ride home if you use them.