XC70 -> How tight can a screw rust? Is that normal, … ?

Hi together, in the course of my last repair (hand brake exploded) the axle stem (back left) was changed. At the same time, I was shown a screw on the defective stool, which was so rusty that it had to be flexed. That was not in itself wild, because the stool was already broken. Maybe what flexing even time cheaper than doing the work, boring the screw or working on it differently …