Recommend o-ring for front of UniqueFire G10?

I bought a FandyFire G10, SKU 91699, from DealExtreme, and a UniqueFire G10, SKU 55243. They appear to have the same body.

I haven't received the UniqueFire yet, but the FandyFire has no o-ring in the front between the lens and the body. Therefore, despite o-rings elsewhere on the body, I don't trust its water resistance. I expected there to be one, but now that I have discovered the truth, I want to add one myself. Glow-in-the-dark would be nice, but I'll use anything that works.

Can anybody recommend an o-ring I could add? Please help, I don't have the ability to measure it accurately, but the bezel outside diameter seems to be the same as my Fenix L2D, if that helps.

I tried to search cpf for posts about o-rings, but search appears to be broken. All I can get is an error message: "This forum requires that you wait 30 seconds between searches. Please try again in 124661984 seconds." I did the math, and I'm not waiting 3.95 years to try again. :shakehead I'm sure someone here can answer this without breaking a sweat...

Update: I have discovered that the o-ring between the body and head is undersized in terms of thickness and does not seal. A recommendation for that is needed also now.

Thanks.

unfortunately without the actual light to measure it's quite difficult to say what size it is. I'm guessing it's about 22mm. Your best bet might be to just buy a few cheap packs of assorted size o-rings (like here and here) and once you know what size it is, you can track down GITD versions of the correct size.