This doesn't sound like something I'd put in my car. It sounds like a bad band-aid, like one made of scotch-tape and toilet paper.

If you're that concerned about what might have been done to your engine, do a compression test. Or even easier, a vacuum test.

Change the oil and filter. Get your hands on some BG M.O.A. (motor oil additive). Nothing else. It's the only one I've found that seems like it works.