Replacement will be expensive
The valve is "frost free" and the basement is finished. Replacement will require a few holes in the walls and ceiling - and the requisite re-finishing afterwards.
I'd like to try other options first...
The "inline" anti-siphon component of my nibco outside water spigot needs to be replaced - or it needs new "insides". I cannot seem to find evidence that it ever existed, however.
It attaches to the spigot with fine threads (probably about a 1" "female" opening) and has regular hose threads...