O-RINGS

[The Baron]

I've seen them on ebay from time to time, can't swear to them being UK though. You have to try multiple search engine variations.

[Sparky]

Here's a guide to taking apart your figs
http://www.joecustoms.com/guide/figconst/figconst.php
http://joes.propadeutic.com/repair.html

and special tips for figs like Zartan:
http://www.joecustoms.com/guide/ztrio/ztrio.php

Several places online sell replacement rings:
http://smalljoes.com/supplies_oring.shtml
though I think they are the same sort as used in plumbing etc? you should be able to find some in a hardware shop.

[plastik]

I just managed to get some o-rings from work (if they're good enough for C-17 Globemasters' then they're good enough for my bust figures!). .

Does this mean we can expect to see Globemasters falling out of the sky because someone nicked their o-rings :