Forget the JB weld- - - -use a product called "Marine-Tex". It's much better than JB where adhesion and leak sealing is concerned. Also, since rust holes are cone-shaped, you're seeing the tip of the iceberg. The hole on the inside is much larger than the pinhole that's visible. I'd suggest drilling a 1/8" or possibly a 3/16" hole where the leak is, and putting a pop rivet in the hole before applying sealer. Scuff up a radius of at least 2" around the rivet down to bare metal with coarse sandpaper- - - -80 grit or maybe even 40 grit, to give the metal some "tooth" for the sealer to grab. Drain the oil and jack up one side of the truck while you're cleaning and patching so you won't contaminate the repaired area with fresh oil while you're working on it.
Good Luck!
Jerry
