Nichols is great, but if you're in SF (or nearby) the other options are Munroe Motors on Valencia St. or Ducati, Triumph, Yamaha of Marin in San Rafael. There are also shops in Hayward and Sunnyvale (?) but I haven't heard much, or much good, about them. Another choice is Dee's repair - she posts on Craigslist, but again, no FHE on the quality of work.