Until replacing with a proper SS plate, we had that problem with our portside fuel fill - PO inserted a non-metric plate into a metric deck fitting. As the tank's contents are drawn out, vacuum pressure increases.
Similarly to an impact driver (which I didn't have at the time), I used a steel punch and 4 lb hammer to rotate the plate . . . did the trick with just a little nicking of the plate's slot. Fortunately I did this at the slip before going to the fuel dock.
True Blue . . .
sold the Nauticat