Ever since my break in (only aobut 2.5 gals. ago!!). Again, I cannot comment on how well it works, but I have to believe it's one of those "can't hurt, probably helps" kinda things.

I had one guy say he has NEVER had to replace his buggy engine sleeve/piston, and I'm talking YEARS of use!!

BTW, I emptied out an old Visene bottle that I keep filled w/MMO (NO softening of the plastic or anything!). It is only sold in pretty large sizes (12 oz. & up), so this makes the process a lot easier & more controllable. Also, the stuff is cheap, about $3 for a bottle that you'll be passing down to your grandkids!

Dean