It’s time to sort the engine. First job was drop the sump. The pump gauze was pretty clean. All seemed quite well then . . .
It looked like a piece of piston skirt to me. Both the pistons I removed were intact but on examination one looked much cleaner than the other. This suggested one of the previous owners had had a problem and just replaced one piston. I thought about replacing both pistons with new ones but as the engine ran so well before I started I decided to leave alone. I can always come back to this if I need to. So back to the engine. I cleaned out the gearbox and cleaned the sump gasket face. Then I fitted a new gasket and the sump.