Well it was terminal. The old Johnson 15hp outboard has ceased to exist. It had overheated in such a way as to make it uneconomical to repair. The cylinders were knackered, the electrics had all melted.
We are now the owners of a nice shiny Mercury 15hp that has only done 4hrs. It still needs running in for another 6 but at least we can still take the boat when we go to Devon again in a few weeks.