Your entire point rests on the idealistic assumption that everyone changes their oil "every 5-7k miles". Maybe this guy did that and if so then he should take your point to heart. But not everyone does that. And, um, used cars. And the "gunk" theoretically ends up in the filter, which gets changed. I would be curious to know about how long loosened "gunk" circulates before it's caught by the filter. Maybe long enough to plug a galley?Never understood flushes. What's being flushed out? All the gunk? How did it get there, and where's it going when it was loosened up? The gunk can only be on the engine surfaces, in the oil, or in the filter. How do we know it worked? And what happens if any ports or channels are blocked by the loosened gunk? A well maintained vehicle shouldn't need a flush, even after 200k miles. Modern oils are so fricken awesome that if the oil is changed every 5 - 7k miles and a good filter is used, you can take the valve cover off at 150k miles and the cams will look like they just rolled off the assembly line. And they're making oil better. Don't know how, but it's interesting.