Head gaskets are supposedly a continuing problem on the M104. Maybe not a problem, but certainly something that can't be fixed once and for all. It's still a worthwhile engine even if it needs a headgasket every 5 or 10 years.
Try Adsit (
www.adsitco.com) for an AC compressor.
Sixto
91 300SE
87 300SDL
83 300SD