So close David...so close. It can be any of the mentioned reasons and I can't recall details of all you've done, but a gummed up fuel filter is the easiest place to check and logical given the conditions you found when cleaning. I think I mentioned the possibility that injector cleaner can knock stuff loose only to have it deposit crud someplace else, and with the gummy conditions you first encountered; this seems a possibility. Would'nt surprise me that if you repeated your clean out sequence you'd find more crud had replaced what you first found. FYI, while my 79' 280ce was sitting for six weeks waiting for a replacement tranny, there was a heavy concentration of injector cleaner and just 1/4 tank of gas in the car. When I got the new tranny in, the car ran rougly for 20-30 miles and then smoothed out and now starts instantly nearly all the time hot or cold. I attribute it to giving the cleaner time to soak and loosen crud which blew out in the first miles. For three weeks now, I've been driving it as hard as I can get away with and it just seems to get smoother by the day. Remember, you have an engine that is known to run better/longer if it isn't babied and that 150 MPH speedometer is there for a reason.