Want to get a new power brake booster, 1973 Duster.

DoctorDiff sells one if you’re not worried about matching the appearance

Bendix Style Dual Diaphragm Booster for Mopars

That said, is the booster working? Because I wouldn’t tear it down and rebuild it if it’s still working.

And of course there’s always just going manual brakes. I had power brakes in my ‘74 Duster and was very happy to replace them with a manual 15/16” master cylinder.