It's unlikely to be a non standard o ring. You can get standard rings from a variety of sources, I use simply bearings in leigh.

Easy enough to make your own O ring, just buy a larger diameter ring of the same cross section, cut it down to the right length and a drop of superglue will join the ends it'll save messing with a sealant. It's a none critical use so any difference in hardness shouldn't affect the outcome. Done it plenty of times using larger rings and/or proper O ring nitrile "cord".

With Hylomar, it does no harm to allow the solvent to evaporate before closing the joint. Maybe not so good if you're on the clock, but that's how it was meant to be used.

.

Predictably enough, Vac appears not to list spares down to o-ring level, but I was curious to know what their pricing might be like … and was reasonably impressed:

**LINK**

https://www.vax.co.uk/spares-and-solutions?product_list_dir=asc&product_list_order=price

MichaelG.

I agree with David on the use of silicone grease. We always used it on the seals of underwater cameras with great success, but there is one proviso. More is definitely not better. A little on the fingers and run the o ring through to just 'wet' the entire surface and then install. Too much and leaks occur. I am not entirely sure why but in the case of underwater use I think it has something to do with the changes in pressure forcing the excess silicone out of the joint leading to voids and very expensive leaks.

Pero

O-rings seal by squashing into a supportive groove, the shape, size and finish of which is important. I guess the grease, being mobile, provides a seal at low-pressure before the O-ring is fully squeezed into place by the camera going deep, especially if the groove is imperfectly machined or is worn. I believe a wipe of Silicone oil also helps keep O-ring rubber supple. However, I think too much grease in the groove stops the O-ring from deforming correctly under high pressure.

Dave

Do a search for the size o-ring you need on ebay. That has not let me down.

Russell