my 1997 p38 diesel auto every so often will come up with gearbox overheat on the message centre then go off again and some times it will do it again and again one after the other i have checked the oil cooler and it looks fine i have checked the fluid level and it is up to the first mark on the dipstick that i am led to believe is the cold mark and the other is the warm mark is this correct/ and what is my problem with the gearbox overheat message anyone help me please