ARO is somewhere between transmission fluid and MMO.Lightweight oil thats good in high temps and acidic environment. I've used Marvel Mystery Oil for over six years. and never had a wear issue. I've got a LST2 with a RB TM728 in it, that I used MMO in all the time. I took it off the shelf after literally 5 yrs, took the back cover off (only an air cleaner was on carb, pipe still in place) and it was shinny like it was last weeks use. put a couple of drops in glow hole and a couple more down carb, turned it over by hand. Added fuel and 5 minutes later it's doing wheelies down the street! Oh yeah, I put a drop on the rod too while the back was open. Granted, I've always used Byrons Fuel and now am using VP, so I'm sure Good fuel helps too.