20 years
I had an OS .46 airplane motor in my shop drawer from 1987 to 2007. No after run oil, no bag, no covers. I took off the carb and lubed it, ran some lube through the glow plug hole, and the next day, I fired it up with the first turn of a chicken stick. Still had the same pull as it did 20 years ago. Amazing stuff, although I don't recommend it to anyone.
You'd think I'd be an OS fan for life now, but with the posts I read on this forum, I really don't know...