Hi, just had the same problem with my 2000 156 1.8 TS.
Found this on another thread - Petrol smell in my 156.
Maybe you've got the same problem, quite common apparently.
For me, it was a spot-on diagnosis from Baz in Brisbane:
There is a basic design flaw in the crown ( top of ) of the fuel pump in the 156
The fuel pipe attaches to the pump at the top via a "Spigot" that is moulded into the crown of the fuel pump. The crown section is divided into 4 sections, with the spigot running through the base of these 4 sections.
Now as the pipe is not supported, it vibrates as you drive, this vibration & flexing is transferred into the moulded spigot which after time fractures trough the base of the 4 sections.
These sections then fill up fuel, overflow & then run over the top of the head of the pump, down the sides of the tank and where ever else gravity will allow.
So if you have ANY odour of fuel inside the cabin or at the rear of the car, pull the rear seat out, take off the fuel pump cover & I bet you anything you'll find the crown sections of the pump flooded and it running down the sides of the tank.
Check it out, I recon you'll be surprized how many people we have coming back with a leaking pump.