My 1997 3500 cab/chassis has recently started leaking fuel under the hood. It only leaks while engine is running and appears to be coming from behind the brake fluid reservoir and near the throttle control assembly (the end closest to the firewall). It is a constant drip not spray. Truck starts immediately on first try and idles fine. This truck sits alot and has only been driven about 100 miles per month for the past year. Any ideas where this may be coming from? Thanks for all replies.

 

Sounds like your fuel return line.

 

X2 When you change it out delete the stainless section of flex hose also just put in rubber! I run rubber to the tank myself.
Brandon

 

If you are going to do it you might as well replace both fuel lines (supply and return) I wouldnt mess with the steel lines go and get marince rated diesel hose and plumb from the tank to the injector pump with that. I beleive it is 5/16 return and 3/8 supply
EVan

 

5/16" return line in red below. Replace from behind the filter all the way to the tank with diesel rated hose and abandon the stock lines.
While you're at replace the 3/8" supply line also, it starts where the red on the right side of the picture ends.