@smorgs,
Quote:No, the floss didn't work - it's worse now.
I forgot to mention this before: ( We were diverted by loose talk about PTFE tape.)
The watertightness of a shower fitting, if it's a screw-in type, is not a function of the thread, but of the washer located at the base of the female fitting.
So try not to muck about with the thread too much. Teflon tape might help, but only functioning as a stand-in washer. You need to try to achieve a solid connection with a sound (unworn) washer. It you can't, it might be time to think about replacing some parts.