996.2 GT3 Petrol vapour smell in cab

[rallyeman]

When my GT3 gets hot, and is stuck in traffic I start to smell, petrol in the cabin. Doesn't matter what I try, AC or windows, close windows AC on, the smell is there. It's not over fuelling as there's no black soot on rear, I've checked for leaks dripping. Could it be, a breather blocked? Any ideas?
Yes I know its worthless now, and someone will offer me £20k haha!