What kind of old Canon SLR?

If it's an F-series Canon (F-1, FTb, etc.), I'd suggest Ken Oikawa. Ken is a retired Canon repair tech who does CLAs'. His address:

Ken Oikawa
28288 West Worschester Road
Sun City, Ca. 92586
951-246-9136

His English isn't the best so he can be a bit hard to understand on the phone, his work though, is absolutely top-notch.

Jim B.