Look here! There's gas floating around on top of the driver's side. It also looks "clean" and shiny (compared to the passenger side).

Upon closer inspection (and a tip from Crazyhippy) the leak is at the top of the dome. Zooming in shows about a 1/8" crack seen in the pictures as a discoloration at the top of the dome.

When the fuel pump is on, the gas is flowing. Even after the pump stops, the gas keeps coming out (as I imagine the system is still under pressure).

VW part number for this assembly is 7L0 919 679. World Impex has a VDO equivalent (the original is made by VDO as well) for under $100. See here.