Lycoming 0-320 Exhaust studs working loose

I have had intermittent problems with 0-320 exhaust studs working loose,
usually with overhauled cylinders. I understand it if I have a stubborn
nut to remove for a gasket change and the stud comes out with it. I
figure that if I reuse that stud/nut again I am asking for it to work
back loose because it is no longer bottomed in the hole. But I just had
another one work loose in flight that was never disturbed from new.

I always wondered why we use plain steel studs and nuts for this
application anyway. It screams "corrosion". Why not heli-coil the port
threads and use a stainless bolt and lock-washer? That way, the threads
are protected from the elements to some degree and using stainless
hardware gives you a little better resistance to rot.

Any engineers know why studs are used on exhaust systems in general?

Thanks,
Mike