When I turn the heater on, I can smell fuel inside the car. Anyone else run into this problem? Kind of curious what to expect before I look into it more in depth.

 

Might wanna check the PD. mine did that.

 

simple. REmove the upper intake manifold, then turin the ignition to the ON position, then get someone to watch both the upper and lower fuel rail and see where it is comming from,
Could be;
Injector O-Rings are shot, (common for 15yr old cars)
PD failure (common on S4 cars)
Cracked fuel hose (common for 15 yr old cars)
one of those is most likely the cause of your fuel leak.