Well in the old days we used to tip it down carburettor intakes and pretend we were ungumming valves (that probably wern't gummed up anyway). The cloud of smoke was reassuring.
There is no list of contents on a REDEX bottle, but if you get the STP equivalent it gives most of the game away. Main constituent: Kerosene..or to you and me, Paraffin...sort of jet engine fuel really.
Does it do any good? I doubt it to be quite honest. These days you run the risk of fouling a vital sensor as well.