Drilled mine a bit off center and made things worse. The key is to start with the smallest and sharpest bit you can and go up a size or two from there (depending on the size EZ-out you use). Drill as straight into the stud as you can. Make sure the pilot
hole is DEAD CENTER on the bolt. Gonna be time consuming but it might save you $$$. If you get it out the exhaust studs are size 8MM X 1.25. Water pump studs for foreign made use that size. Stainless would be a plus. Anti-seize them also just in case.