German Car Specialists in San Antonio. They've done maintenance and modification on all of my cars since 2005. They built two highly modified Audi's for me. They specialize in Porsche, Audi, and BMW. They've done quite a few ESS SC installs on M3's, go to their website
https://www.mygermancarsa.com/ and check our their resume. Should I decide to mod this car (not really likely, for personal reasons completely unrelated), I wouldn't have anyone else do it. They do all my maintenance, too, because BMW of SA sucks so bad I won't even take it there for the
free maintenance. I'd rather pay GCS.