on seacocks with no leaks. There is no need for 5200 if you had the through-hull and three bolts holding the seacock. I had to remove a couple after the polysulfide was fully cured, and found an internal pipe wrench from McMaster Carr (where else) easily removed the through-hull after which there was no problem removing the seacock with no damage so was able to use the same parts again. I agree with other posters, 5200 has few uses on a boat beyond sealing the ballast and fixing leaks in inflatables and other repairs.
If it helps you, DeBond does work, it will take awhile to work its way into the thin layer of 5200.