Kevin, I first started using some of these additives back in '92 when I bought one of the first Ford Explorers. Can't remember the exact brand (Prolong?) but that engine had 128K on it when I sold it. But I'm such a stickler for changing the fluids often and keeping the cooling system clean, so it's hard for me to really determine if the additive actually helped or was it just the regular maintenance? It probably didn't hurt though.
My last three acquisitions (a one owner '02 Z06 that had 19K miles, a new '09 Nissan Rogue for the wife and a '02 Camaro with 52K miles for my oldest son) all I have done is keep the
oil and coolant fresh. We'll see what happens over time.
-Dean
EDIT: Actually I used STP
Oil Treatment back in the late '70's on my first car ('71 Camaro). I'm not sure if it helped, but everyone that was a motorhead told me to add some so I did.
