The operative word there is "almost." Anyway, I have a pile of motors to assemble with arms back from grinding/balancing. The first five went smooth with no big hassles (well, I was out of the springs I wind for the Mabuchis, so I had to make a little side trip to spring-winding land).
Then I got to an old Mura NCC12 where I used the old arm/stack and comm after stripping, to keep as much of the original DNA as I could. I did the same stock wind, left the timing in place, the only difference being that I had the arm balanced and a light "skin" grind done. No matter what I did, the motor runs warm and draws more current than it should. It runs smooth, but just doesn't run well, and I tried all sorts of things with no change.
So... it goes back into the "drawer of parts." Sometimes a motor just doesn't want to be built.