In case this is helpful to anyone, there is a very nice independent BMW garage in Bad Zurzach in Aargau - they're called Zurzibiet Automobile GmbH
Ocostrasse 20, 5330 Bad Zurzach
Phone 079 633 14 39
When I used to have an older BMW, I was always searching for a good independent garage. And, voilà! - now that I no longer have an old BMW, I've found a nice independent BMW garage
But I thought I'd share the information here, in case it's useful to anyone!
I can't comment on their BMW repair abilities, but I bought some winter tyres from them, and they were great - they matched the price from e-pneu.ch, and fitted them in half an hour while I waited. All very efficient, and I organised the whole thing with them by e-mail. For me, it was worth going there just to leaf through their great collection of 1980s/1990s BMW brochures in the waiting area