If you ever happen to be in need of a mechanic in north-west Iran, I can recommend one in Zanjan. This is not a place you'd want to go unless you had to, but you'll pass by it on the way from Tehran to the Turkish border.
I was lucky enough to find two experienced and friendly guys who did a good job on my Enfield - they even said they'd seen one before when a German bloke passed through. They don't speak a word of English, but they know their stuff and charged me rather little.
I have their card but it's all in Farsi so I can't tell you the address! It's easy to find, though: start in Enqelab Square (the main square of the town). One of the four roads from here goes downhill. Go down here, and after about 200m (shortly before you come to the next junction), their workshop is on the left.
By the way, the hotel right on Enqelab square has underground parking. I paid seven dollars for a single there.