[ERA Chas]

Sorry to hear no real success with the problem.
Perplexing problem and you've about exhausted all the usual suspects. Interesting about the piston-to-shim contact. I'll watch mine as well.
Deferring to Bob of course, I agree about trying other pads. Hope you hit on the right ones first try 'cause time and $$ add up.
Excellent idea about wiring the attach bolts, you'll never think about them afterwards. I paint-stripped mine but will wire next time as well.
Please keep posting progress and good luck.