Stop in for a cup of coffee

clue to the mystery perhaps? It’s the only water jacket that has yellowing around it, and it faintly runs down the block a bit. Further, the carbon ridge at the top of the cylinder, isn’t present by that jacket. Bore scope down the water jacket shows just a bit of mustard, all other jackets are clean. Cylinder wall shows no obvious cracks inside the jacket or the cylinder itself.

Now to try to build my pressure tester.