OK, you're putting some pretty good annual mileage on your truck, which I think you have mentioned before...
Can I ask how your DEF consumption is?
From the pics, I am guessing your latter suspicion is what I would guess = small hole in the accordion pipe where DEF is weeping thru and soaking that mesh jacket.
The flow of liquid combined with a constant heat/cool cycle of the exhaust system from driving has created the perfect environment for rust.
The entire exhaust system gets hot according to the EGTs in FORScan, so me thinks you have pretty good science fair project going on here w/title: Environment to create accelerated rust
2018 Ford 150 PS Diesel Platinum FX4 in Ingot Silver w/BuiltRight Rear Seat Release, Gatorback F150 Splash Guards, Lloyd Custom F150 Luxe Carpet Mats & Titan 40 gal replacement fuel tank
FORScan mods: Auto Start/Stop Disabled, Bambi mode, Digital Temps Above Gauges, DPF Full %, OCR (Operator Commanded Regen) and Heated & Cooled seats on Home screen
Last edited by jmperlik; 10-11-2019 at 03:05 PM.