You ARE most fortunate. Most of those guys have gone away, the diagnostic equipment being so expensive, and i don't trust most of the old diagnostics on the new computer driven cars.
I used too have one, and, as you, I could just leave it and he would fix it.
I have given in too taking mine too the dealership. Yes it is a bit more expensive. It is also worth the money as I can be assured, to a large part, of it being taken care of.
I have a good relationship with the Ford dealer that I bought the Ford from and, too this point have been well satisfied. I treat them as my old mechanic, they have earned my trust.
Now I recently had a problem with the ABS break system, it showed up on my consol as a problem. Took it in and they could't make it do the same things it did when I took it in. Murphy's law I guess.
Blessings