I can't tell how far up the tube the switch thread is but looks like it could have been screwed up to far past the the tube threads
This is only a possibility but putting it in the freezer can't hurt as a measure to see if this might work, but be careful not to mess the threads up when trying to unscrew the switch, maybe use some needle nose pliers
Its stainless steel so might be a bit more forgiving than brass or copper
One more thing is that it could of been cross threaded / forced when screwing the switch in but that's not something you wouldn't realise your doing as that would be quite hard to do
Hope you can get it sorted
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