Problem Solved/Thanks

I found an o-ring at the hardware store.It wasn't the 1x18mm size though.We tried several sizes at the store and found one close.Also got one of the Dr. Scholls small round corn pads.It fit perfect on the Pos. end of the 123 battery.No more rattle,the switch feels snug but turns with just a little resistance.It feels perfect.I put some silicone grease on the 0-ring.I put the light in a sink with about 8 inches of water for 15 minutes and the inside was perfectly dry.So thanks for all of the suggestions,this is a great forum for help an advise.