ATF cleanse
As I understand it from my dad, and we all know dad is right!, ATF is more of a high detergent oil and will dissolve more crap. I was taught to add a quart of ATF a little bit before you're next oil change. This way, 4 quarts of oil don't get wasted or used very shortly.
Another product that has been used for years, is Marvel's Mystery Oil. This is amazing stuff.
-Dave