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................PTFE tape was utterly useless and I ended up using Sikaflex to seal and hold them in alignment.
Suggest you try Loctite 55 pipe joint sealing cord. It's made from PTFE, but looks like thin string, and you don't need very much of it to seal a connection. Best to try some of it out before you start the actual job of fitting the skin fittings to the valves to the hose tails. Unlike thread tape where you may have to use several layers to get the joint to seal, this stuff will do the job with just a few turns in a single layer. But do try it first to get the hang of it. The Loctite dispensers come with a thread cutting device which makes cutting the cord easy.
I agree that the valves are significantly more bulky than those originally fitted, and on my B36(2002) when it came to fitting the 1.5 inch heads overboard valve and skin fitting, it was quite a performance because the 90 degree hose tail could not be fitted last as it would not clear the edge of the cupboard door under the wash basin. It meant attaching the 90 degree hose tail to the valve and tightening the elbow into place, then while one person held the valve/elbow assembly close to the hole for the skin fitting, the skin fitting was then passed through the hull and the internal washer and securing nut then screwed loosely on to the valve/elbow assembly and for the skin fitting to be turned and tightened into position. Then the skin fitting securing nut was finally tightened into place. I used copious amounts of sealant, and today when the job was finally completed after the sealant applied last week had hardened, I used a high pressure hose to squirt water at the hull fittings and up inside them to the shut valves, and there were no leaks. . . . . . . . . so far !!
