I do believe we have a winner, making Trev29 my current savior if so. I'm not sure how I missed the multiple threads from the past on the caliper half mismatches.

Took at good look at both front calipers under a strong light tonight. They must've been around the block a few times because neither shows any punch marks near the separation lines, top OR bottom - they just aren't there on either of them. This might explain why, when I pulled them out of the car and did Bruce's bench test that I found through your link, BOTH of them came up with halves mismatched!

Not terribly impressed with Cardone remans right now, I can tell you that much. Assuming I replace them and everything works out, I'm out a silly amount of time and close to a couple hundred bucks with the new master, caliper paint, and many quarts of brake fluid I've put through the thing chasing this issue around.

Live and learn though - I should have delved deeper into the resources here, and sooner. And at least now I know the state of the master cylinder before I send the car and lady friend out into the world.

And I won't feel like quite as much of a hopeless idiot...

Chris