Gavin is good, but can be difficult to get on his schedule. He's not the quickest to respond to email inquiries (understatement) but if you get him out he knows his shit.
Rick from Rick's Game Repair is easier to work with, and knowledgeable as well. I know Rick well and he's a great guy that also knows a ton about video game repair. Last I knew (5+ years ago) early 80s stuff was not his forte. I'd probably focus on 90s and newer.
I've also used Phil from Arcade at Home in Romeoville. He is friendly and good as well. Was much easier to get out here, but I also live close to Romeoville, so YMMV. He seemed somewhat more expensive at the time, but that can be hard to gauge when people come out for different issues.
Anyway, these are the 3 I have used. I've been happy with them all, and I would probably rate their expertise in the order I have them listed (although Phil would bump ahead of Rick for 80s stuff).