My MOT has come back with three advisorys - leaking shocks, treads down to 3, but the one that worries me is that they said the rear of my fuel tank is badly corroded and will need to be replaced within three months, which will cost me £800 in parts and labour. Is this a normal thing to happen to a car? I've never heard of it before and i'm a bit frightened as to what might happen if I can't afford to have it done.