Enjoying all the information on this site as I'm new here. Working on reviving an 87 pu slant 4 speed manual 2 wheel drive. I'm slowly converting this over to hardware more of the 70's ie. earlier carb and switch over to hei ignition setup. When checking for a leak the other day I barely tightened the very rear exhaust manifold stud and I felt it turn so easy, not good. Sure enough it's stripped now and coolant is leaking out. I can remove the stud and the threads are fine. Tried thread sealant no good still leaks and now an exhaust leak as I can't get it tight. Is there a fix for this without pulling off the manifold? and if not is the preferred fix helicoil or tab to next larger size stud.

Thanks