I did see that page but none of those matched what I have, mine is an alum, cap with threads with a star type indent in cover, I guess I will stick with what I have, managed to get cover loose with chisel, will just have to keep not so tight. harbor master says there's a lot of these caps on the bottom next to water fill up.
The aluminum deck fill & cap assembly is discontinued for the very reason you have discovered. This from Ward Richardson at Beneteau:
"The Beneteau Deck fills have recently changed. The old version aluminum fittings and parts for them are no longer available. They have been replaced by a new stainless steel version.
Deck fill water SS Part Number 129432
Deck fill diesel SS Part Number 129433
Deck fill waste SS Part Number 129436 Dia 50mm Hose
Deck fill waste SS Part Number 129435 Dia 38mm Hose"
My water cap is swimming with the fish next to the boat. A water deck fill assy cost roughly $55 delivered to my door.
And yes, the water and waste deck fills are designed to be opened with your winch handle or specialty wrench.