Back in the 60's there were a number of products available, some established with dates way back to Fred Flintstone. STP, Justice Brothers, Gunk, Lucas are a few I can remember. STP, Motor Honey and various fuel and crankcase additives. Back then non-detergent oil was still used by many due to its lower cost and old habits hard to break, like using the newer multi-grade or multi-weight oils. The quality of many less expensive oils lacked the additive packages the big oil companies would put in their oils. This caused a buildup of gunk on the interior surfaces of the engine...lots of paraffin, too. So, to address the issue they created an additive with high detergents to put in the crankcase and run for a minimum of a half hour, or driven on the road for a day or two just before the oil would be changed. We called the engine flush "Engine Enema". I think there was a product using that moniker for their engine flush. It could clean a little too good on some gunked up engines and cause clumps fo flake off and plug the head drain passages, even the internal machined oil passages. Our station refused to use anything that acted like the engine enema for that reason. Decades later the snake oil appears to be still enhancing the bottom line for some businesses.