One of the mechanics at Mossy VW in El Cajon owned an ALH until it was totaled a few years ago. I can't remember his name, (I want to say Leon or Larry... except those sound so stereotypical for mechanic names!
) but they're pretty good about letting you talk to the service techs there. As far as dealerships go, Mossy VW is one of the better experiences I've had. I've only dealt with the service department, though.
As for Service, the "Trusted Mechanics" list in the TDI 101 thread lists one shop in Escondido, in Northern San Diego County. Otherwise we're still waiting on a guru to emerge down here as far as I know.
...I'm excited to be corrected, though!