Do you replace, grind or polisc your tension discs, when you notice some wear on them? I studied my tension discs. You can turn the disc until you get the right light direction for looking. This is my close up picture of one of them: You do see some grinding marks from the thread. I do not think, that I have got any problems using them. Then I compared to a picture I found on internet, and those discs seems to have been weared even more: https://oldsingersewingmachineblog