From personal experience, I recommend Mr Hunter's suggestion. Emotionally, it can be highly rewarding.
Several years ago there was a rash of engine oil theft from the boats berthed around me. Everyone had a good idea of who the culprits were. A tube of valve lapping paste mixed with a gallon of fresh oil removed all doubt.
Best part was that the engine rebuilder didn't suspect sabotage so he didn't flush the oil passages. Three months later, a relapse.
To this day I still savor the memory of all that smoke pouring out of the stack.
