Sadly, the rusty Midwest is already imposing its will on our 5 year old Fusion. While detailing the car last week, I noticed that along the rear side of the inner portion of the rear doors, the pinch welds seem to be rusting/bubbling from underneath. Think of it as where the outer door skin wraps around the edge until it reaches the inner side, then terminates. Surprisingly, the bottom of the door, where everything runs down to, is clean. The rust is on the vertical portion of the latch side, and there are little strips of bubbling on what looks like the pinch welds. What's the best way to stop this? I don't want it somehow spreading to the outer door skin. I cleaned the areas well, and rubbed a little 3-in-1 oil on them until I figure it out.