Air isn't the problem, that's for sure.
I do want to verify those pad p/n's, but right now I can't.
Paint caused the pistons to stick? Maybe, but that would have been apparent immediately as well (as a lack of fine modulation).
Unless there is more, I'm still of the opinion that the root cause for this is the installation by the shop, with the mounting bolts being the major contributing factor.
I'm positive that there were signs, but who knows at this point.
Focus on a thorough, proper repair and lesson learned.
As for the pads, go with the Z26s this time, they are well known and proven by many.