Back in the 70's I worked in a gas station part time. The station owner told me Marvel Mystery Oil was nothing more than ATF, and laughed at folks who bought the stuff, but he loved to sell it at 5 bucks a quart, pretty pricey back then. I had not heard of the stuff again until I joined this list a few years ago, and found a lot of folks here swore by the stuff. A few months ago I had a lifter that would bleed down if I let my Westy sit for a few days. It would take anywhere from 2 to as long as 15 minutes for it to quiet down on start up.  So, I tried some Marvel Mystery Oil-the problem has gone away. It's made me a believer in the stuff. YMMV.       Jeff