Actually the knobs are fine, it is the whole braking mechanism which is smashed, the bit under the knobs that goes around the frame & screwed onto the blades, all four.

He could have unscrewed the knobs for transit, the bare metal screws the knobs screw onto would've withstood the knocking about much better without the knobs. It wasn't packed well.

Sure, I'll buy new whatever's needed, once I resolve this through Paypal