This evening I removed the subway ramp under the play field for the first time since I've owned my WW (it's been 13 years, but it's also a very low play game). I'm working on getting to the less accessible areas to try and track down the source of the black filth that's getting tracked across the rubbers and play field. This is a project that I actually started when we first got the pin and ended up stopping at dissembling the upper play field and the subway ramp.
What I noticed when I removed the subway ramp was that the play field underside, immediately over the subway ramp was blackend pretty much along the length of the subway run, with the worst around the entrance to the mine VUK. What truly surprised me though was that whatever this was - it wiped right off with a clean dry cloth. No scrubbing needed. The ramp was pretty dirty too, and that I scrubbed with my Millwax and a toothbrush (I'm out of Novus) and that cleaned up pretty well.
Any idea where the black filth might have come from? I'm sure there is some degree of carbon buildup as part of normal usage and the machine has never been fully shopped as I essentially bought it just days after it came out of the container from Europe. But I also can't see any other accumulation like this under the play field. I figured if it was normal wear and tear that the entire underside would be coated, but it's not.
Next, up working up the courage to disassemble the upper play field and potentially replace the ball popper in the multi ball trough as it sometimes takes an extra pop to launch the ball out.