I had it replaced under warranty back then and haven't seen it rusted since.Im having the same issue, sole owner drove it right off the lot and notice the nozzle started rusting about 7-8 months ago. Right now the entire nozzle is rusted.
Outside humidity won't cause it rusted. What I meant was that the humidity in the tank caused it by water vaporization from fuel. Just a thought.2016 model. mine sits outside under a carport at all times. zero rust in the filler. i live in the Northeast so it's humid here. just another data point
If your fuel get quite warm it will pull moisture into the tank. And if your truck is sitting for a while the moisture will collect on the filler neck.
My 06 dodge had rust on the neck and it was from that.
Used to drive back and fourth from bc to alberta and the truck would sit sometimes for a couple weeks at a time it's amazing how much moisture will build up in the fuel.