Lol, i've fixed so many systems with the brown tar color. I find windex to be a great cleaner for this. Although I hardly smoke. My ash tray will be filled with cig butts but I'm lucky If I get a drag or two from that one cig. I get to tied into a game and forget about the cig. The only major problems with the cig tar is on monitors. Like last week I cleaned my cluster server's monitor, when I finished cleaning it and turned it on it hurt my eyes, Too bright.
Other then that it doesn't hurt the PC it self. Just makes it look ugly.
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To live is to let die