I've got a Wolff recoil spring in my P6 and want to replace it with a new factory one. The only place I've found one is the Sig factory store, as part of a parts kit for $24 - not really that bad, but I'll probably lose the other parts before I'll need them. Wolff advertises their springs as replacements for the 225, 228 and 229. Can I ASS U ME that factory recoil springs will interchange? Not that I've been able to find factory recoil springs for the 228 or 229 either, but it'd be good to know.