BILL!
I remember as a boy, putting a bunch of CrabApples down the exhaust stacks of trucks that parked next to where I lived, and how much I always enjoyed the sight and sound of those SOOTY apples flying out of their exhaust stacks when they gunned the engines right after starting them up!
I would be real surprised to find that you haven't seen trucks with DRY black soot caked all around the tips of their exhaust stacks...
Next time you do, watch how much BLACK smoke comes out of that rig as the driver leaves your line of sight...
And of course it smears, it's diesel oil! Diesel is much oilier than any other form of fuel, it was designed to be! Now, don't get me wrong, you are right, a diesel with bad valves, and/or a bad oil leak from the engine or even the transmission will produce an ideal environment to collect more soot, and will stick more than just regular poor driving style soot will. But that soot hasta come from somewhere! Soot is primarily composed of unburned diesel fuel combined with diesel exhaust by-products. Oil blowby, and poor valve adjustment is one thaing, but bad truck drivin' is another, 10-4? Now, don't y'all make me get out my training materials I have out in the garage!
And Bill, I ain't got no damn soot on the back of
my car! Thank You Verrry Much!