Engine knock on semi cold start?

[Greenie]

One of my first full time jobs was at an Esso gas station - 2 active bays. We had a customer with a dodge slant six come in with a minor operational complaint (can't remember what) and the station owner put a quart of Rislone engine flush, let it run in the yard then did and oil change. The sludge must have been holding that engine together because after that we saw that car in for a variety of engine issues. I'd be careful with the flushes...