I wanted to follow up on this. I added 8 oz of Kreen to my 07 @ 226,256 miles(owned for 190,000 of the 226,000). I have used Valvoline ML 5w30 for the last 80,000 miles and Puralator 1 filters. The oil change intervals are 3,500-4,000 and I do it myself. Oil is normally dark when drained, driving is mix of highway and town.
The oil was black when drained. It seems to have eliminated any lifter ping at start up. It also seems to be running better but that could be my imagination??
All in all, it seemed to have done some good. We'll see what the color of the oil is at the next change.