Rust under door sill protector

Hi Omnibug, I use a product called Fluidfilm, you can get it at local auto parts or off Ebay, comes in a spray can with a wand like WD-40, but the oil is sticky like chainsaw bar and chain oil. You apply it after the weather has been dry for several days, so the seams between sheet metal are very dry to facilitate capillary wicking action.
Under your car are a bunch of small plastic plugs, especially in the rocker panels. You put your car on a lift and spray in these places, and inside the door bottoms, and anyplace else you see rust. 1 can does a whole car. No need to sand and paint the rust, it will stop in it's tracks. Good luck! Robert

 

Once the rust has started, it needs more preparation than just rustproofing.

You need to use a "rust converter" to stabilize the rust. A phosphoric acid converted will turn the rust into iron phosphate.

Then, you can apply rustproofing.

 

How easy was the door sill removal?

(and thanks for the heads-up)

 

Yeah, I had a look, using a putty blade with masking tape. there's 3 tabs. Also helps a bit to pop-up the plastic sill trim partially, and pull up a bit on the rubber gasket. Our driver's door one looked fine. Maybe being that you're in the snow belt, getting a lot of moisture on that ledge with salt as well. Thanks again for the tip.

To your gripe: a lot of trim pieces are like that, meant to protect, and end up promoting rust. Door protection strips for example, especially the ones with similar body openings for clips. They're really out in the weather, rust-prone.

 

These areas are traps for water and salt laden electrolytes and every form of water absorbing organic detritus.

Whenever I get a new car, within days, I spray these cracks with a thin rustproofing into these cracks.

Transtar Body Tec Amber Rustproofing 4423 | eBay

Dust, salt, dirt and organic detritus gets between the flexible plastic and the metal. It's like the paint and zinc reust resisting coatings "sand off" the protecting paint and zinc layers.

Waxy rustproofing acts as a lubricant on which the flexing material slides. It also keeps moisture laden salt from entering.

Body panels are well protected by zinc coatings and painting. It's the join arrears that are most vulnerable.

The spray cans comes with small wand straws like WD40 cans. It takes almost no special skills to apply. But, it does pay off a lot in the long run.

 

I'm not quite understanding, are you thinking it's been repainted? There's no way factory painting would be done with weather stripping in place. Not the end of the world, but good to know.