94 Cavalier 4 cyl fuel odor from engine compartment after shut down?

I have a 94 Chevy Cavalier base model 4 cylinder. About a month ago I began to notice a gasoline odor that begins to become evident about 15 minutes after shutting the car off. Over the last month I think I narrowed it down to the engine compartment and more specifically the area around the fuel pressure regulator for the fuel injector rack.

I don't smell anything when the car is running and fuel ecomomy hasn't been effected. There isn't any sign of any external leak except for a damp residue on the top of the fuel rail in front of the #4 injector but it doesn't smell like gas when I try to rub it off on a cloth. Strange thing is that the residue comes back after I clean it but I can't tell where its coming from.

Has anyone seen this before? Is it due to a leaking o-ring on the injector and if so, can the o-rings be replaced separately? Is it much work to pull the injector rack? Is there anything else you may think coud be the cause?

Any thoughts would be appreciated