Agree with willis on the sympathy thing. Gearbox oil can take a while to heat up, way longer than the water which is what the dial n the dash shows. Personally, car needs to be running for 10 mins before exceeding 4000rpm and a good 15-20minutes before hearing the beep. If the car has been driven hard before the oil has had time to heat up and therefore lubricate then faults will occur.