As for fuel cap door locations, they vary from product-to-product for a number of engineering and packaging issues. There are no government regulations on the subject of left side or right, so our engineers place the fuel filler on the side that makes the most sense.  The only relevant government regulation, in fact, is that no fuel can leak in a crash test. Considering that, the decision on left or right becomes a packaging decision.  In the Flex, for instance, the fuel filler is on the passenger side in part because the mechanism for the power liftgate is packaged on the driver side.  Because the fuel filler location varies, we clearly identify the location with an indicator in the fuel gauge—which hopefully reduces an awkward moments for our customers at the gas station!  And while we’re on the subject – could you find the fuel filler nozzle on a 1956 Continental Mark II?  Talk about awkward moments!