LOL. Forget all what I said about calipers. Jumped in the car today for a 100 mile drive to Leicestershire, expecting to enjoy some fine weather. Got about a mile before it was clear something was wrong, when trying to pull up at a roundabout. Front wheel, with the pattern caliper, red hot. Nursed it home, though it seemed fine by then. Revert to the XJ8.
Sigh, now do I attempt to clean up what is probably a rusty piston or not bother, and just put on another disposable one. Brand new sliding pin. Lasted just over 3 years (Feb 2021) and 6,000 kms. No hint of anything at the November MOT. Car had sat for last 3 weeks on the drive as I was repainting the boot lid in the garage, and wanted the lacquer to get a good cure.