Chassis distortion due to heat. Likely story!
You can lift one corner of a bare chassis by a couple of inches or more before any of the other three corners move.
Perhaps galvanised Morgan chassis last too long and are converting to pretection that has a reduced life span. Then perhaps Morgan are going to ensure that they are the only source of replacement chassis and prevent anyone else making them, even for obsolete chassis. Then a price hike.
Or perhaps I am becoming cynical in my older age!