How opportune this should come up. I just this afternoon got back from 'the Factory' to amongst other things get my core fixed. I have, I think, one of the very first made. Not much glue was used then, more was used later on and then the assembly changed a bit so the parts no longer unscrew. All versions perform the same, just the early ones might unscrew if someone gronks down hard tightening the cap or battery on (it has 'reverse threads' so it unscrews then).
Anyway, the fix is really simple. Strip it down to those two parts and clean the threads with ISO if not clean already. Then a small drop (enough to fill the threads at a single point) of:
http://www.loctiteproducts.com/p/cntct_usns/overview/Loctite-Stikn-Seal-Extreme-Conditions.htm#
The advice is do it when you're through for the night so it can sit overnight to fully cure. Other, similar, products have had issues with heat and grabbing too quick on assembly but 'the guys' cautioned it's still not a good idea to boil this part (nor the switch). The core should be removed.
So, anyway, that's the story. That's the stuff they use and recommend. They said for guys that really want to be sure, a second drop on the other side buys a lot of insurance.
OF