If you're getting gray goo in the pressure line, it's from the baffle in the muffler "fretting" or vibrating, and the wear particles are mixing with the oil.
One of the best things you can do with the overly restrictive Evo muffler is ditch the baffle. You will get more power, and none of the gray goo...and still have enough muffler pressure to the tank. It's only marginally louder.