We have a B39 built in 2006 and the Seacocks/ Thro Hull fittings are definitely Brass. The 38mm Seacocks for the holding tanks became very stiff, so over the summer I replaced them with reinforced plastic assemblies made by Trudesign. This is a huge improvement- they are feather light to operate. I thoroughly investigated the condition of the old assemblies & despite some pinkness on the outer flanges the brass was still very solid, so from an integrity point of view they clearly didn’t need changing.