You have a tiny spot and your going nuts? Man, I had holes large enough to pass my fist through in the back side storage compartments of my 745t, and the driver and passenger floorboards required me to rebuild the floor with hardening compound (I did the same to the rear).

On a quick sidenote, I recommend ALL VOLVO OWNERS continuously check the back of the front wheel wells (which is also the floor of the driver and front passsenger) for deterioration or wear every 3-6 months. I have an early 700 (1985 745t) and have come to the conclusion that the front wheel well is one of the design flaws of the 700 series. Many other automobiles employ two surfaces in this space; a full wheel well that comes down over the back of the front tire and a separate driver/passenger floorboard distanced from each other by inaccessible space, similar to the hollow area behind the front side fender.

Volvo's driver and front passenger floorboard IS the wheel well. Why is this bad? Because it directly exposes the floor of the car to all the crudoo, stones, salt, and other garbage that the tire shoots off at high velocity. This can easily damage the thin protective coating provided, and expose the metal to air, wear, and rust. This is a cause of many a wet floor whose source owners are unable to discover.

As for your problem, I suggest you get ahold of some sandpaper or an orbital and go with some wd-40 and go at the rust headfirst. Get down to the good metal, prime it, and then seal it with some clearcoat. Nothing works quite as well as the orbital sander to take out the rust. i recently went over my whole car with it and eliminated all body rust I could find.

Good luck,
Rick