Duncan,
This saga has gone on so long that I find it a bit strange. These Lycosaurus engines are pretty much bullet proof, any engineer and his dog in this aviation business should know all that needs to be known about them by now.
I've never heard of the term "ring chatter" but would assume it means worn ring grooves, rings moving up and down in the grooves, piston slap is not the same thing, that's worn sloppy pistons swinging side to side as they move up and down the bore. This engine has been stripped apparently more than once?
I'm beginning to think someone is pulling woolies.
I've had a few faults in my own engine, stuck needle valve, half dead magneto, worn valve guides. And in every case the fault has been identified correctly and fixed correctly with no further trouble.
I don't know what the maintenance regime is on N reg or if the a/c is in UK or US, but I would recommend a word with my LAA engineer, in Tranent.
I don't even know if he is allowed to advise/look. If you want a third opinion PM for his details.