I've got a 112 from what I'm guessing is the mid-90's (serial number starts with F2). The nut is notched and to look at it, it looks just like all my others. But the wrench that works on the rest doesn't work on this one. Not the round notched end, not the square notched end. Is there a third notched option? Anyone know where I can get the wrench to fit it? Again, this is NOT a smooth nut.