Mike: You bring up a good point with the manifold (and injector) seals. Mine never leaked so I dont have firsthand experience with that. But your stumbling issue does sound a bit more serious than what I experienced due to an over-rich hot start (and maybe more serious than "Mr. X.")!

It almost sounds like your cold start valve is engaging and "Sticking" or leaking somehow. Maybe a bad water thermo-time switch or aux air valve, too? If I were you I'd unplug my cold start valve and see if it made any difference before any warm cranking (the way you say you have 10 mins makes it sound like once it thinks the engine is cold, it will turn it on, thus flooding the engine).