If the brace is rusted, then the sheetmetal of the fender is also rusted behind the brace. I bet if you hit the lower part of the outside of the fender with a sandblaster you'll find rust holes happenning there. What I've done with mine is to remove the outer fender sheetmetal just below the bottom body line, and then you have access to the inside of that brace, which is where the rust will be worst. Once you have access to the inside, sandblast or grind the rust away, replace any part of the brace that needs replacement, use some sort of rust inhibitor or just epoxy primer and some paint, then replace the outer fender sheetmetal with a piece of good replacement metal. That brace very seldom needs to be completely replaced, just parts of the lower portion, but if you don't do the fender sheetmetal now it'll ruin your new paint job within a year or two when the rust does come through. Hope this helps.
