Take advice from my misfortune and perform a thorough inspection and cleaning of the integrated mudflaps/body trim on your wagon or sedan.

For years I believed this design would eliminate the body cancer so prevelent on pre-86 models which have the mudflaps hanging about 6' behind the wheel arch, leaving the lower body panel exposed to stone chips.

In that regard, yes, the paint is protected.

Consequently, I never knew any periodic maintenance of the area above and behind the flaps is necessary.

But rust through is *LIKELY* if you don't clean out the dirt and stones accumulating up on top of the newer mudflap.

There are many chambers and crevices up there formed by the moulded flaps and body trim panels. Some are there to provide drainage from this hidden area, as I mention below. But they clog.

Behind the flap there are two slots, about the size of a large screw driver, located on the front center of the plastic trim panel the curves down to integrate with the mudflap. These are the drain slots of the body trim panel.

Make sure your poke a screwdriver up into each one to dislodge built up storne and dirt. On my '86 wagon, I got a duspan full of dirt the poured out of each side.

If you, too, get such a discharge, I'd bet you have a ton more still up there.

My advice: remove the mudflap for positive inspection and cleanout of the body trim panel. Also check for rust on the lower compound curve of the body at the front of the spare tire holds.

The mudflaps are held by a one plastic rivit top enter. You'll need to replace with new rivits. Next, two 8mm bolts and washers are removed from the mid-body of the flap. Finally, the inside edge of the flap is help inplace by a large metal clip that fastens to a body seam flange near the frame.

Be sure to also check for rust under this clamp, as well.

If any of your undercoating is cracked and crazed, inspect and probe for scale, loosness, and underlying rust. If rust is found, you'll need to remove the undercoating and repair the metal. I find Corroless anti-rust paint a good choice, because it likes to hold fast to rust that has been scratched clean with a wire brush. Recoat with a rubberized undercoating.

To remove the undercoating, I find a propane torch kit with a wide angle head will soften the material for easy scraping with a 1' putty knife. (maybe Santa will give me a Heat Gun for Xmas!!!) After you get the heavy mass off, use a low-fuming oven cleaner to help clean off the residue still sticking to the good paint surrounding your rust problems. Eastwood Company sells "Under Gone" which claims to remove undercoating. I disagree. But it does help clean up the area after the heaviest of the coating is gone. (It smells like oven cleaner, hence that recommendation)

My hope is you will have discovered your rust while it is still surface rust, and not have to cope with the insidious cancer affecting my car.