Please can anyone help Im not technically minded but here goes. For the last few days Ive had a strong smell of petrol, and have now noticed fuel dripping from under the car drivers side just in front of the rear wheel. Looking underneath theres a silver can type of thing that it appears to be leaking from. Odd thing is this stops dripping about 40mins after the engine is switched off but soon starts again a short while after the engine has been started. Any ideas what it is, and is it expensive?