If I remember I can take pictures and measure when I get off work. I am hull #256 so I expect ours will be the same. It was smaller than "standard" but a common/standard size for RV's.
That said, have you looked at getting it out? I was not able to without serious cutting of fiberglass. Even through an access hole that had already been cut. I could reach it, but there isn't enough room for a wrench. I replaced the hose and shower head from the new unit, and left the old faucet.
$5 in washers from the hardware store and it works good as new, although still looks ugly. The challenge is that you wouldn't be able to bring the old washers into a hardware store, and its doubtful a hardware store in Portugal would have them. I can attempt to measure them but don't have a good set of calipers on board.
Also, the shower faucet and sink faucet are completely different. They look similar externally, but are a completely different mechanism with different washers internally.