pre-90:
171 951 221 - low tone - 31.68+VAT
171 951 223 - high tone - 31.68+VAT
post-90:
3B0 951 221 - low tone - 40.88+VAT
3B0 951 223 - high tone - 40.88+VAT
Not sure on the difference, I guess its just the type of plug connector used. I beleive the low tone horn is the one behind grille, high is behind wing.