Most pop-opens are not original, even if it came in a Ford box with a Ford part #. The original caps were discontinued during the 71 model year, and a soft recall was done for owners to "fix" thier cars by swapping the Mach 1 cap for the regular spin-on cap. Apparently the caps did indeed pop open....especially in rear-end collisions, allowing fuel to easily be ejected.
The NOS caps were LONG GONE for many years, until Ford reintroduced them as a replacement part in the early 90's...with an "update": an internal screw-on cap was added inside the ornamental flip-cover for safety reasons.
Enterprising aftermarket suppliers provided parts to convert the new version back into a 100% correct copy of the original version, but then the mounting bosses molded into the inside of the flip-lid on the new cap, neccesary to mount the retro parts was removed on updated versions so the conversion parts could no longer be easily attached.
Most of the caps today are the new versions.
In all my years of ownership, the three most difficult parts of these cars to collect were traditionally the gas cap, the 71-72 sport grill and the 71-72 eurathane bumper.
The gas cap and grill made glorious comebacks years ago...where is that damn repro eurathane bumper we are all waiting for?
