Threads like this are abundant and easily searched, but there is a ton of debate.
The basics as I recall them for this topic are that:
-
some o-rings don't like petroleum products and better safe than sorry but check with the manufacturer,
-
pure silicone grease
usually will do the job well (available in plumbing supplies, auto supplies, scuba dive shops, Lighthound, etc., etc.),
- any lube application should probably be proceeded by a good cleaning of all the surfaces to be lubed,
- less is more works well for lubes and will keep crud from collecting a bit less,
- WD 40 ain't for lubing lights and/or o-rings,
- Wax based lubes might work for threads but I would not use them on o-rings myself,
- DeOxit is a contact cleaner and will remove oxidation from contacts but is not a lube, and
- Too much heat is a bad thing (duh!) for lights and lubes.
As always, YMMV, but here's what I do -- every six months to a year (or if it feels like it needs it), I disassemble the light, clean it with a clean shop rag, cotton swabs (being careful not to get lint in the threads), and a little alcohol if needed. After that I hit all the contacts I can with DeOxit Gold and let that dry. This includes batteries after they are checked. I use silicone grease sparingly on all the threads and inspect the o-rings and lube those. I put 'em back together and don't worry about them. Works for me and has for years. The only problems I have every had are batteries dying (Ya know, they tell me they will do that from time to time as the light gets used. Who knew?) and an old style SF Nitrolon G2 twisty tail cap came apart.
I use the lights I have a lot, some live in the car year 'round, and while I do have backups (not too many since I am a very poor man) I don't recall more than one time that I have needed one. That last bit of course doesn't include when someone has to borrow a light and is usually right after they ask why I carry more than one.
Again, for more details, discussion, rumors, and arguments on this topic, try any number of searches.
