The sending unit lines always rust out, which is unfortunately a dealer only item. And if that line is rusted, most likely most of the screws holding it on will snap and you will need a new tank, or extract a bunch of broken screws from it.

May get away with jb welding the hole in the line. Replacing gas tanks is probably the most PITA thing to do on these trucks, but still not too bad since these trucks are easy as hell to work on.

http://www.scerbfab.com/carb_faq.html