However, I can mention that Junipero Serra Porsche & MBZ in Daly City is a shop that I like going to --- in case you need a backup place to go to.
They are exclusively* a Porsche and MB shop. Although they are not MB only, they do, count among their repertoire, various 300SL Gullwings, air-cooled 911s, Pontons, etc. I've known Jimmy, the proprietor, for several years --- he's a hardcore car guy and personally runs an SLS, a Gelandewagen, a 993, and a 3.2 (I think). He mentioned to me before that he has about 20 E500Es under his care. One of them is a silver 500E with 22K miles on it. I got impatient waiting for the owner to decide to sell it, so I purchased the red one that I have now.
BTW - thanks to this thread (Gerry) for publishing the contact information for Robert Fenton. I was also trying to contact Robert a few weeks ago but ran into the same issue --- the internet was saying that his business was closed, and his published phone number wasn't working. Now I know how to contact Robert.
* BTW I don't think they work on 944/928/968s. I've only ever seen air and water cooled 356s/911s there. I might be wrong.