For the scooter I completely trust Mr Zhang. He's the guy Bikefarm's Jeremy used to work with before he got his own place. I'll try and get the address next time I go there, but here's some directions in the mean time. Heading South down Roosevelt, go past the roundabout intersection with Jilong Rd. Pass one road on your right, and the next intersection is on the left, with Xinglong Rd. Do a U-turn here, and head back up Roosevelt. The shop is then on your right, at the bottom of the stairs of a pedestrian over-bridge.
I can also second this recommendation (I think we're talking about the same place).
The address I have is Roosevelt Road, Section 5, Number 27.
But, Bri, I have always called this mechanic Mr. Chen. That's also what it says on the business card he gave me (Chen Rui Cheng). Gee, I hope I haven't been calling him by the wrong last name all these years.
Also, not to quibble about the directions, but do you really have to make a u-turn? At the first intersection you come to (traffic light) you can just pull over like you are making a left-hand turn and then drive over to the tire shop when the light turns green. From there, you can walk your bike on the sidewalk to Lao Chen's.
Anyway, another hearty recommendation for this mechanic and this bike shop. You will probably need some Chinese ability here, though, which is perhaps why some people prefer the Bike Farm.