Try Brooks Berdan, who has a service center. He has a good full time technician who has worked on Macs for years.
He isn't in So.Cal. but I think one of the best, if not the best, and by far most reasonable is Terry Dewick for vintage McIntosh gear. I believe he lives in Tennessee and can easily be found with a google search. I would at least call and talk to him before you decide on who you wanna use. I know that is who I will send mine to if it needs help.
I recently had my C712 cleaned and a new volume control module installed by Mike Zuccaro. McIntosh factory authorized service technician:
Antique Audio & Radio Service
8795 Corvus Street
San Diego, CA 92126
Luckily, he is only about 20 mins from where I live. Hope that helps.