Yeah get that old stud out, then get a new one. Then do yourself a favor... buy a bunch more of the nuts for your flanges... you will need to double nut the new stud for installation but then double nut the rest of your flange nuts. Will prevent you from loosing any more studs.
I have been double nutting the exhausts on the bikes I work on in my garage.... I have lost a few myself before doing this.
