US hardware retailers seem to have bigger ranges than Australian retailers, but the stuff I got from a big retailer here (for tap washers) was brownish rather than clear so I bought some online. It was easier to buy online than visit a specialist shop, and you only need a tiny amount.
I’ve been using this stuff for a couple of years now and it seems to do the job.
http://flashlight.nitecore.com/ACCESSORIES/Others/SG7/
I use silicon, either the paste, liquid or spray depending on what i want to put it on.
I used to use Vaseline on maglights as that was what was recommend dont know if it still is anyway i found it broke down the orings and certain plastic bits of the maglights over time
Krytox. If you can afford it, its the best possible grease for knife pivots and o-rings that you can buy.
A little KY always seemed to make things slide well 
J/K… I use a little tub of silicone grease, probably from Harbor Freight or an auto parts store.
XG-12
I just spit on em.
A stick of butter. 
You use it on your O-rings?
Mayonnaise :+1: 
Lady juice :smiling_imp:
I’ve recently had good luck with Master Plumber Faucet and Valve grease - waterproof, heat resistant, designed to be used with o-rings, valves, washers, etc. $2.99 at True Value Hardware.
I’ve compared it to Syl Glide, white lithium grease, dielectric grease, and others, and it seems less sticky, and more slick. The store rep said it’s silicone based, but you’d have to verify that. I like it. Mag recommended Vaseline. You likely didn’t do any harm, but you’re probably correct to switch to better.
After re-installing the ring, I’ve always used Hoppes 9 gun oil instead of grease on the threads, after cleaning them with alcohol. Things seem to spin together better, especially on Maglites.
Zen
I use XY-2 silicone grease. One of the cheapest I could find.
Though I’m trying to arrange a shipment of XG-12…
Any silicone based weatherstrip conditioner will work. I been working off an 8oz tube of Silglyde I bought 30+ years ago.
The stuff also works great for re-conditioning door and trunk seals, A little dab goes a long way when spread with a sponge application.
For threaded with o-rings, I use a soft bristle toothbrush
The WD is short for Water Displacement. WD40 is not a lubricant. It will clean your O-rings but it will also dry them out if not lubed after cleaning.
I've had the debate of WD-40 with lots of people over the years. That it's a lubricant. Nothing sticks to it because it evaporates.
WD-40 gets used on my fishing lures and baits only.
I get more lubrication rubbing a finger alongside my nose and rubbing it on, then with WD-40.
YMMV
Principal at work: Like dissolves Like.
- Some O-rings are petroleum-based. These are generally black, somewhat firm to fingernail pressure, and not very stretchy.
- Some O-rings are silicone-based. These can be various colored, a bit softer to the fingernail pressure, and a bit more stretchy.
Yeah, there are a whole lot more but for the most part with lights this is what you likely have to deal with.
I know, not very scientific determination, but we are working with cheap lights here where they fabricate performance statistics. Probably most of the time they don’t have a clue what O-ring is bring used and it may change depending on what bulk shipment they got from wherever. I doubt you are ever going to find out.
For threads….metal on metal > use whatever grease or lube you want. Use sparingly, and try not t goop everything up with it.
But, most of the metal threads end in at a O-ring. If you are using the wrong lube, you may end up compromising the O-ring over time.
Not a critical O-ring, not a big deal. You may not even actually need it….so who cares.
I, on the other hand, am a scuba diver. My lights and my cameras are $$$ and those O-ring need to be clean, properly lubed, and taken care of, or I pay the price. Literally.
On petroleum-based O-rings you can use silicone lube.
On silicone-based O-rings you may be able to get away with petroleum lube….but those come in so many different formulations it’s a headache to sort out. I just use a ‘universal lube’ (generally damn expensive; Christo-lube, Tribolube) or one that I KNOW is formulated for silicone, generally less expensive but not terrible (stuff that comes with my camera equipment).
A small amount goes a long way so even an expensive tube is not that big of a deal.
Screw it up or don’t know, some hardware stores have a decent stock of O-rings. Then you know you can use silicone grease.
If it comes out of a spray bottle I wouldn’t trust it.
WD-40 is not a lubricant. It’s a [water displacement] and a poor lube.
For older lights without anodized threads in the tailcap, i find that candle wax does the trick best.
Use the softest candle wax you can find, which will stick to the aluminium and smear rather than crumble.
Unlike any other lubricant, it doesn’t dissolve the aluminium, so you don’t get that awful grey gunk you normally get, even with lumpy silicone grease.
True story.
WTH!! Hands on experience, HUH!!