Thanks. What is the o-ring I need? I can't seem to find on OCUK site. Do they have them?
Difficult to say for sure. It depends how tightly the tube compresses against the o-ring once it's inserted. I would always err on the side of caution and get a replacement o-ring since they're cheap, as it's not worth risking a leak whether it occurs in the near or long term.
If its just the G1/4 end, I have a bag of Bitspower O rings, not sure if its allowed but would be no hassle to throw one in the mail.
Ahh, I'm not sure, actually looking at the picture is it the sealing ring, inside the fitting or the screw end ?, I guess the internal one, so I wouldn't know if it would work, but as others said, I would probably just change it, I think it was Greebo's thread above I was just reading and his lovely pool of red coolant under the PC after 2 weeks, better safe than sorry.