verbs: unvoiced sibilant

verbs without sibilant softening:

[s]: lease, release
crease, decrease, increase
grease, degrease
cease, decease, surcease
fleece
produce, adduce, deduce

verbs with sibilant softening:

[z]: please, use, abuse

[s] spruce (v), loose (v), refuse (n,adj), close, closer (adj,n,adv), noose (v,n), voice (n,v)
[z] ruse (n), refuse (v), close (v)