We are stuck with "Chateau California" gasoline here, which in addition to being more expensive, deteriorates rapidly.
I finally broke down and bought a new carb, as after I reinstalled the old (now clean) carb, it just wouldn't run right.
I think the "gray slime" I described after the 24 hour carb dip actually was metal removed from the carb body. It probably enlarged air passages, the slide housing, and a bunch of other things so that now it won't run properly.
By the way, a new carb was about $20 on Amazon!
But, on the the bright side, I got a new ultrasonic cleaner out of the deal!