Not just the streaks, it used to clog the valves as well. And people still wanted to suck it into their lungs ???
In my old outfit, during hangar maintenance, the outflow valve was removed and put in a bucket full of fuel for 24 hours.,That got rid of the tar. IIRC, we were one of the first UK airlines to ban smoking. People said it would cost us passengers. In fact, the opposite.