Arominus

I had the same problem with my 924s, as it turned out the hoses on the plastic expansion tank on the top of the tank itself were leaking. I replaced every single hose in the fuel system in the back of the car and it solved the smell. My tank was not cracked. Of course my car was hit 6 months later and now my 944S has the same problem but stronger in smell, so i'm going in and replacing all of those lines again.

SalzundPfeffer

Did the plastic expansion tank have any leaks? I'm planning to pressure test them both with compressed air and a bucket of water for good measure.

I'm seriously considering removing the breather valve too when I'm all done. There is way too much flex in the tank before it checks open. I may experiment with two one-way check valves in parallel, reversed, to replace the valve, granted they release at a lower pressure. I don't want to have to fix the tank again, assuming I can fix it...