I had only one experience at sills & it wasn't too good. I took a front wheel with tire for them to install a new one. My machine is an R90/6 with left side brake. The old and new tires had directional arrows. Apparently no note was taken of the rotation direction on the old tire & thus with a 50/50 chance they got it wrong.
Anybody could make a mistake like that...I just didn't appreciate being rather rudely spoken to about it as though I was being overly picky about their work. Funny thing I never sought service from them again. In fairness this was some time ago.
One other time I had been in the sales room while a salesman was explaining the differences between the "boxter" engine vs the K.