[cycleguy55]

Well, I thought I had it sorted out. I had the car up in the air and had occasion to turn the rear tires by hand with the parking brake engaged. Passenger side was locked tight. Driver side, OTOH, still turned. WTH!!

To make a long story short, I discovered the brake arm that actuates the brake was missing the attachment nut. Gone. I checked the nut on the passenger side and it wasn't anywhere near as tight as it should have been. 7/16" NF? I thought these were 'metric' calipers! Bleeder screw takes a 7/16" wrench. Huh.

Anyway, replacement nuts were installed with blue Loctite, as the exposed stud isn't long enough for a nylock nut or lock washer. Shame on GM for that oversight, and shame on me for not installing them the first time with Loctite.

Moral of the story: Even when you think you've found the fix, check and double check to make sure.