92015-1958 NUT,12MM
It’s not left handed. The OEM nut differs from what you can buy at Sears in that it’s thinner, but you can use a regular 12mm metric nut. You’ll have to figure out the thread pitch (I don’t remember), but that’s not hard since generally there’s standard pitch and fine pitch. Just buy one of each at the hardware store. Oh yeah, this is one of those nuts that you’ll regret it if you don’t use loc-tite (but you’ve already learned that the hard way ;) )