The pump is screwed by scews and copper rings not by nuts
That's the original cause of the problem. The threads in the case were never designed to have bolts screwed in and out the metal is too soft for that. That's why the factory used studs. I am sure you can have a new threaded insert put into the case (they are available in a variety of inside and outside diameters) and then install a stud or rather, install FOUR studs and secure the oil pump that way. Maybe use an industrial epoxy to secure the stud, too. Don't use bolts straight into the case