Yes, I've heard of this. I recently had a VW Passat with the 1.8t that had developed the infamous VW sludge buildup problem, google if you've never heard of it, but it's bad. While researching the problem, I read many rumored solutions to fixing/preventing sludge buildup; from a kerosene flush to ATF to Auto RX, none of which seemed to be a definitive fix. From what I read, kerosene had the best detergent properties but you may risk breaking apart huge pieces of sludge that may get caught in a pickup screen. After doing the research, I pretty much decided it was ridiculous to put anything other than motor oil in and took the car to carmax and sold it. This seems to be a fix where the older engins operated at lower tolerances than today's engines. I'd tell your friend to drain the oil after 3K miles and fill it with high quality synthetic oil and a good filter and repeat in another 3K miles, and so on...

And as long as the engines aren't prone to sludge buildup then you don't have to worry about it.