I had a seized caliper piston as well after purchasing with 222k on it. Driver's rear was mine too, but that's probably coincidence. Have you tried re-bleeding by chance through the fittings? Could be an air pocket in that caliper if only that one is stiff.

Could be the bearings at the wheels just need some lubrication, too. That would make them pretty noisy. Grease the fronts by removing the ABS sensors. Since you've had the wheels off a lot by now you're probably getting really good at it.

You're right on the ICP connector.