Got myself a cheeeeep ebay LED torch with a variable focus which simply works by pulling the lens away from the LED. My plan is to fix it at a chosen focus to help stop water ingress, and I noticed the lens rattles a bit suggesting that the lens also needs a bit of waterproofing. What are you people that make lights use to help waterproofing? Guessing some form of grout would be ideal but just wondering what other people are using

Would ptfe tape work? Less of an issue if you need to disassemble the torch at some point in the future.

Self amalgamating tape. Waterproof & sticks to itself.

That looks pretty much what I am after for fixing the focus, but what about getting in to fix the lens. Tape would be very awkward for my fat fingers

silicon sealant, maybe? You could still get that off in case you smash the lens.