The nut that holds it on is starting to dig into the spindle. It's almost burrowing into it. I needed to use a washer to keep nut from going any further. Still, it was plenty tight and I even had a jam nut up against it before the main nut. the main nut was indeed a nyloc nut already. So a torqued, nyloc nut using red Loctite. After the first time this happened I would pull over every 10 miles to check it to make sure it wasn't coming loose again. After a while I got complacent and would not check it. Sure enough it happened again! Each time I was running full speed and coming into a turn, I would let off the throttle, the sled would slow down, then BAM!! the front end nose dives to the right. Both times it was on pretty hard packed trails so the sled simply slid to a stop. Point here is to never assume your front end or anything else for that matter is tight. I'll be sure to check this before I go out everytime now. I'm sure had a I checked it before I went out I would have noticed it was loose and probably could have avoided it. Still think a cotter pin would be nice here.