I've cleaned up engagement surfaces but there wasn't much to do on them as they were already pretty smooth to begin with. The rebound slides I've seen on new guns were black which appeared to be Teflon coated(?) the wear was even and minimal on them. However the rough action on some guns was due to metal flakes/residue and dry crude. I've changed a few parts that apparently left the factory in that shape. If it's a new or new to me gun I clean and inspect them for any uneven wear. After a few range sessions the insides get another cleaning and then it gets decided if they need anything. Polishing the suffices smooth will not improve much if anything there is more damage done to guns from people that like to polish the insides or play gunsmith.