Got very lucky with a fix and it came out better than expected & I'd like to share. Have seenseveral posts regarding the horn buttons falling out from 2000 Disco II and equivalent.My buttons still had all tabs, but I would bet this would work even if 1 is missing.

supplies:
silicone sealant $4
2 #17 O-rings or #18O-rings $1
surgical/sport tape

1)Remove buttons carefully after removing 10A fuse 16 from engine compartment block
2) Remove springs and carefully tape back top contact plates being careful not to stress connection
3) Carefully fill each center cup (spring seat) with silicone and re-position spring in sealant, holding gently in-place with surgical tape
4) Allow sealant to cure (partial is fine - this step just helps with keeping the spring cooperative during replacement)
5) StretchO-ring over top of button and allow to roll down to tabs (if missing tab, you may need to secure ring with sealant or mechanical means such as a small screw.
6) Gently re-seat top contact plate into button, making sure locating tabs are correctly positioned- cementing is not necessary
7) Gently, but firmly press button back into steering wheel hole - top first or bottom first.

Once seated, the buttons will not drift laterally and thus will not pop out. The #17 will lead to a firmer button and the #18 will lead to a somewhat softer touch. I like the #17 because it is very secure. This has been flawless for a week or so (which would have been roughly 7 annoying searches for parts at my feet as well as annoyed looks from my fellow New Yorkers as I'm honking my horn.

Good luck.