Ours was rusted out and leaking around the threads so I bought the one through CD. It is a slightly larger pipe thread, so you will have to get the appropriate drill bit and tap set. Easy to tap in fiberglass, however, I will say I had ours out on a bench, fully removed, after taking out the galley cabinetry.
On the other hand, if the threads are good, a new bronze nipple and mini ball valve of the original diameter would be much easier. I used 4200 as thread sealant thinking if it failed I would end up buying a whole new muffler next time.
Rob