A long-overdue update...
The car arrived (had it 3 weeks now). I got the Cooper fuel door AND the entire hinge painted (didn't want that black spacer visible on a silver car). I installed it easy enough, just a PITA to get the flexible part off and back on over the metal gas funnel mouth opening dealio. Anyway- got it on (slight "reshaping" to the protruding metal tab on the left of the body needed) and it was just wrong. I lived with it for a few days and asked some friends and everyone agreed- it was just wrong. While it looked great on my Cooper, this just wouldn't do on my S. So, I removed it and re-installed the S cap and hinge. The Cooper hinge is cheesy plastic too- very flimsy. Oh well, at least I tried and now I know which way I like it better.