i like mystery oil too. I dump a bottle in the crank case just before an oil change... Usually, the morning of, drive around all day. then drain it out. its kinda gross when you see what all comes out of a nasty engine...
Sea foam works better through a vacuum line...
I really like that lucas fuel injector cleaner. it says to put like 3 onces or something, but I use closer to 9-10 in a tank of gas, its the only cleaner that I've used that seems to make a difference as far as injectors go...
I don't recommend doing it at every oil, but a good motor flush goes a long way to clean gunk. The best one i've used is the CRC high mileage motor flush. It comes in a metal can. otherwise that one that advance sells isn't too bad either.