To share a tidbit - when I pulled the front fork oil at 13,000 miles, it was the color of graphite. I used a Turkey baster with a length of tubing on it to evacuate the old fork fluid through the top, and measured the old fluid into a plastic measuring cup. I then took a lint free cotton diaper, taped it to a long clean wooden dowel, and wiped out the tubes. The diaper drew out pretty much all the old fluid, and a bunch of the gray graphite looking stuff that was clinging to the tube sides. As others before me here have suggested, I mixed some 15 & 10 weight into a 12 weight type mix, and put back a just a hair more fluid than I took out. I can only guess the graphite looking stuff was as a result of a spring end being less than flat, which may have caused the spring to twist slightly upon each impact? The left side was worse than the right, but both were dirty.
