84' rear axle flange bearing replacement

I have recently begun the process of changing one of the rear axle shaft flange bearings on my 84' 300SD. However, when I got to the point of loosening the slot nut I began having problems. It seems that no matter what I do I cannot get the nut to loosen up. I was able to get the nut to rotate 5 mm or so, but at that point the nut seems to be completely seized. It almost acts if I am rotating the nut in the wrong direction. Can anyone confirm to me whether the slot nut is a right hand or left hand thread nut? Any advice that anyone could give me would be greatly appreciated.