While mine doesn't leak at all (untouched from new AFAIK), I suspect they are prone to damage on installation if one is not exceptionally careful. Reminiscent of Triumph twin rocker shaft O-rings.
Anyway, I buy these sort of engine bits from vtwin.parts. They usually have decent stock of gaskets for the x-wedge. Can't find the o-ring in the x-wedge catalog, so can't look up the part number or size specs on Vtwin.parts
