One of the issues is the presence of higher quantities of ethanol blended into 98RON fuel in France, but this is also a factor in the UK now as well.
After on trip to Northern France in which my car became almost undriveable I was advised by a French Morgan owner to avoid taking 98RON , especially at small low volume stations. The problem was traced eventually to a bad batch of fuel which contained larger than normal quantities of water (among other contaminants) , this upset the Air Mass sensor and the resulting backfires destroyed the structure of one of the catalysts.
Since adhering to the 95RON fuel (Eurosuper) I have had no problems.
OK I would prefer the higher octane diet, but it is not really a problem in most modern machinery , and I think that all the range of engines fitted by MMC back to the 1990s and beyond (?), unless modified, will run quite happily on this fuel.
