I have to say that I am pretty sure the disc has little to do with the black rubber.

We have a game on route and had the launch party yesterday. The game now has a couple hundred plays on it with NO black marking at all.

What is different about our game compared to others? Well, the first thing we always do now before even playing the first game is we remove all the CRAPPY black rubbers that come on the game and install translucent/ clear rubbers from PBL or now from Titan. We do this on the bottom half of the pf at minimum and for sure the flips, slings, and main posts.

We have NO black streaking after many plays so I have to think changing the other rubbers in the game are more important than anything.

did you switch out all the other game rubbers from black to something better?

Ours looks super clean still. Granted you probably already have 3 or 4x the number of plays on yours because we do not have the player based you do, but still that looks really bad.

well, a couple hundred plays on the one on route (black disc still in the game, but all main black rubbers have been changed out with translucent) and all is good. Changed one variable and the symptom went away. Granted n = 1 so we probably need a few more to start making any real conclusions.