So rather surprisingly, the newer back arrived from France (Posted Saturday and arrived Thursday. . . while Royal Mail takes the same time to deliver a small packet from 60 miles away . . . ) It should help diagnose the problem - if it works, and the older one still produces problems, then I Know its the back. If the new one produces similar, then it's somewhere where the on the body where it meets the back. I'll keep you posted, just building an order for