I think Rajaie would agree that the inner elastomer o-rings are the ones that fail. The outer teflon rings probably don't change shape or size very much, so if the inner supporting/compliant o-rings could be sourced this might work fine. I have a VANOS o-ring that I keep meaning to measure and guess what size it used to be. One difficulty is that removing the teflon rings is tricky without damaging them since they have tobe stretched quite a bit to get them out of the groove. Teflon does have a good 'memory' though so they will probably be fine if they don't get any nicks.

I think Viton would be a good material given the heat and oil, but I'm not expert - does anyone know what would be best?