after the "usual" weathering techniques(powders, chalks, paint, etc.), ive also had realistic luck with real sludge. simply go out to ur personal vehicle in the drive(unless its brand new), and swipe ur finger along the oil pan, block, etc. apply to the engine and there u have it. oh, and please dont do this right after driving the car. i shouldnt have to say that, but theres always that ONE guy out there... haha hope this helps.