Do your checks if you live where they spread salt in Winter

also, as stated above, pull your rocker plugs and use a good creeping corrosion inhibitor, Fluid Film, Woolwax, Surface Shield, Cosmoline, Corrosion Free, etc... the creeping action, can get between the sandwiched metals and protect from the inside out, as well. Ski

 

The rust proofing company my truck goes to every fall to be sprayed uses a thin corrosion inhibitor inside panels and sprays in those areas. They actually even drill a few extra holes to spray into as well. They use a thicker solution on the undercarriage.

 

I am spoiled, I do my own so, I know those areas get covered. I just cant trust another soul to as good of job as me, for this. I pull all the rocker plugs every fall, and HOSE the crap in there in a 360* pattern. I do appreciate this thread, as it made me go to the garage, and pull my sill plates and look. mine are clean, dry, with no corrosion (2019 30k miles, garage queen, rarely out when nasty). But, still... I applied fluid film to the length of the seam on the front of the rocker, below the weatherstrip, and put it all back together, tonight. peace of mind.

I think what happens here is, sand grit, from the road, our shoes etc, gets in, under the weatherstrip, and starts to chafe the paint, like sandpaper. once through the finish, the rust starts. even with weekly washings in the winter, if you dont clean and dry the door jamb areas, this grit starts it's "magic". I think that is why the Service Bulletin states to recover with protective tape.

Hope this cures your ail's. again, thank you for sharing this with us, so we can take a look at ours. Ski