replaced as it isn't a normal o-ring. It has a tab (or two) that run into a hole drilled through the idle screw. I believe that was done so that the seal does not rotate around the threads while adjusting the screw. There could be a replacement out there, but it would have to be a very specific type of seal, not just your standard o-ring. I would take it off and take some pics, but I'm affraid I would damage it trying to get it off. It may be designed not to come off at all.
I'll give the silicone treatment a shot and report back.
