Marshall Services in Waukesha does good work (Acura of Brookfield send all their body work there). They are located near the Sam's Club in Waukesha.......I can't comment on them specializing in German cars, but they did a great job on my CL a few years ago.
I have also heard good things about Mander - also in Waukesha - across the street from Stay Tuned (I think they give our free loaners).