[KTL]

Clean the receiving female threads with an actual thread chaser (don't use a typical high speed steel cutting tap for making brand new holes, for the M6x1.0 sump and M8x1.25 cam housing holes) or make your own thread cleaner by cutting lengthwise slots with a fine cutoff wheel in sacrificial bolts.

Use a low strength threadlocker like typical Loctite blue and sink the new studs all the way down (or as far as they'll go w/out excessive effort) and back them out a 1/4 turn.