Replacing the drums will not insure the new ones will be true.
When my trailer was new I had some brake problems mainly bad grease seals from the factory.
When I pulled the drums I noticed they did not show even marking on the drum surface.
Had a local machine shop check them out and three of the four were not concentric. By that I mean the drum surface was not concentric with the bearing bore. The machinist had to cut a fair amount of drum surface to fix the problem.
But after the brakes were much smoother operation than before.
