2004 Vauxhall Astra repeated p1372 crankshaft sensor code

engine warning light keeps illuminating if i pass 3ooorpm, then goes back off if i drop below 2500rpm. fault code is logged as P1372. replaced crank sensor with two genuine ones and fault is still there. car drives ok though. have been told by a friend that a field remedy exists for the Z18 engine to cure this. is this true and what is involved