Oil questions

I've heard that trans fluid is a good injector cleaner. As far as oil cleaners, are you talking about the age-old idea of engine flushing? I personally woukd think with today's engine technology. It's a waste of money, engines are built with more exacting tolerances and more involved breathing systems that limit the intake of outside influences. As far as sludge buildup in engines, there are a couple of automakers with known excessive sludge buildups that have warranted their engines for these issues. Oils today are far advanced from yesteryear, regular changes should, in my book, suffice. As a sidenote, years ago we would flush our big v8's with kerosene, we always heard about the risk of plugging return ports, never had the problem. Also we would dump Marvel Mystery Oil into the carb until the engine would stall, let it sit for a while, refire it up in a huge cloud of smoke, supposedly cleaned out the top end of the engine, don't know if it actually did, but the cloud of smoke over the neighborhood was something to see, pollution wasn't on anyone's mind in those days