Just for something to think about, I've seen engines with worn bearings leak through the bearings with similar results:
- The grey color of the oil was from minute metal particles in the fuel
- The hard to get to run was due to running lean due to air being pulled through the bearing, resulting in a hard to adjust needle
The one thing no one has mentioned yet has to do with the outside of the engine. Is there fuel or oily residue on the outside of the engine anywhere after it was running?