The BENETEAU part number for the water deck fill assembly is #129432, Stainless Steel, Osculati . The European manufacturer is Osculati. My understanding is that the entire assembly is required; the cap isn't available.Secondly, there is no part number for this It is not a standard fitting part…
Again, verify that info with Ward Richardson at Beneteau. Price it & obtain availability from Murray Yachts, Annapolis Yacht Sails or other Beneteau dealers. Or, you can order directly from Osculati (good luck with that). And again, you can always replace the entire deck fill assembly with an SAE deck fill from any local or online marine chandlery. Good luck!