Before any major job, I always skim my faceplate. Since the initial one, a skim of 0.002″ (0.05mm) cleans it up very nicely.
It takes my lathe, on very slow feed speed, over half an hour to complete the facing operation, but once done, it is spot on for any work I want to do on it.
People seem to think that items like faceplates and soft jaws should last forever, but to me, to get the required accuracy, they are eventual disposable items, with a life of maybe 10 to 15 years, so get trued up and recut every once in a while.
John