97 Yukon

Got A 97 Yukon With A Slight Valve Tap At Idle..will A Lil Marvel Mystery Oil Work Or Jus Deal With It..got 99k And Runnin Castrol Syntec ..also I See On Some 97-99 Burbans The Back Windows Go All The Way Down Is That A Mod Or The Yukons Are Jus Not Made That Way

Not much help, but I can tell you my 96 Yukon back windows also only go down 1/4 of the way. Annoying. But I imagine it should be pretty easy to 'mod' this... There are probably hard stops put in place so the window can't physically go down any further (to prevent lawsuits and little kids getting heads stuck in there and foot on the rocker power switch), but you could probably easily remove those 'hard stops' to allow the window to move further down.

(I won't try it, I have a kid who would probably stick her head in the window and do something like that)

It won't hurt to put the additive in to see if it helps, it not well then if it bothers you that much you will have to replace what ever is making the noise.