I'd leave the blow torch as a last resort. Before that, I'd probably try:
1. Soaking several days with repeated applications of penetrating oil.
2. Repeated boiling water treatment.
3. Some taps directly onto the screw with a hammer/screwdriver to break whatever bond there is.
4. Cutting a new groove in the screw to hold your screw driver if the channel is beat up (dremel tool).
5. Praying. Hey, it can't hurt if you're willing to take a blow torch to the barrel..... smile

Good luck.
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Thanks,

Fisherdan