I may have missed something, but right now I can't find anything better than seki for black if white plays elsewhere.
I'll give it a try: ko?
off course is the natural shape, but here it doesn't seem to work. That's why i tried first.
is actually a little tricky as black may be tempted to play in the above diagram himself, but that seems wrong:
Hmm, ok, I can't see anything but approach ko now. So not sente until the (late) endgame.