Sealing a window to concrete cill

[Triassic]

We’ve had heavy driving rain and as a result water was been driven under a uPVC window. The window was originally sealed using silicone, which on closer inspection has hardened and come away from the concrete. Any suggestions on what I should replace it with?

[Hobbiniho]

polysulphide sealent as it stays flexible

[Mr Punter]

Compriband