To replace or not to replace.
Dear friend, On the face of it, all this talk of straight vs. tapered can be a bit confusing but read my post again while looking at photos of the parts in a West Marine catalog and all will become clear. The threads I spoke of are the ones inside the ball valve when turning it onto your existing through hull fitting, not the threads under the large, existing nut. Do reconsider replacing the entire installation now as opposed to half today and half a year from now given the relative ease and simplicity of doing the whole job after removing the large nut. By the way, in most cases, getting the nut off will result in destroying the existing through hull fitting anyhow. Consult a West Marine Catalog by searching for "mushroom through hull" and you'll see that they sell for $13.99, probably less expensive at your own local, privately owned chandlery. When you get down to it, it's chump change and a matter of knocking out the old fitting, quickly cutting and sealing new pads before the fact and installing the new ones. It should be noted that the pinkish color usually shows up after removing the fitting from the boat in the area between it and the edge of the fiberglass hole and up into the area covered by the nut. Hope this added info helps you make up your mind, Glyn Judson, E31 hull #55, Marina del Rey, CA