I had the same problem and managed to remove it with gentle heat and WD40. It took maybe 10 or 12 heat cool cycles over 2 days with WD40 applied from above or through the air bleed hole. No use from below as it won’t get past the O ring.
I devised my own method of applying heat by fabricating a copper collar soldered to the end of a 25W soldering iron. The collar fitted nicely over the boss on the carb body which acted as a heat sink preventing the solder from melting. It could be safely left for hours. This gives you an idea the temperature reached wasn’t too high.