Recently the engine has been dropping onto 4 cylinders. It took me ages to find it checking all the wiring. Eventually I discovered a poorly crimped connector on the B side of the low voltage loop. Discovered the problem almost by accident when I was about to buy a new coil. The give away of the source was the rev counter died but the engine kept running.
Moving onto the clutch slave cylinder and the water pump which are really the only problems that are left over. You can see the tiny split in the connector where the wire doesn’t quite reach the end. As the engine got hot the gap widened and the system collapsed. Bugger to find but thankfully a simple fix. I didn’t have to buy a new coil either which I was about to do.