Just a heads up on this, my
boat has these same EZ Deck Fills. The caps
sold by Force 4 are incompatible with the seals that they sell for those caps. The new caps have a small upturned lip at the end of the bayonet and the flat white seals will not fit under that lip and so won't seat without assuming an oval shape. Also, these flat white seals look a little different than that black seal with the step that you have pictured. That black seal was also the original on mine.
We ended up using a knife to trim off the upturned lip, and then the white seal will seat properly, but I'm not sure if it will provide a watertight seal as we've had
water ingress following the change.