Got any pics? Do you have over sized tires that like to throw stuff down the side of your jeep like mine does? Its probably just sediment from the road, but it can be tricky to clean without the right stuff. What I found works is 303 Aerospace Protectant. Its made to clean and protect vinyl and plastics from sun damage, and works pretty well. It took all of the mud stains out of my factory soft top and I imagine it will do the same with your trek top.