I think this could be the solution:
Now White can do nothing to prevent Black from making two eyes.
nando: White is left with the -
exchange which should be used later as a ko threat.
Playing is impossible, because White can capture Black.
A play at will be answered by
and the situation is a seki.
Axel
unkx80: So far so good, except that saying that the last diagram is a seki is wrong. Because of shortage of liberties, Black is dead.
nando: Indeed, Black can do nothing against White playing successively a, b, and c.