Fluid Leak from Drawbar Mounting?

After scraping years of crude from around the rear differential on this '50 8N, I found hydraulic fluid leaking from the driver's side drawbar mounting shaft. I put a wrench on the nut and found the entire shaft turns easily but will not tighten, nor can I make it unscrew all the way. It just seem to turn freely inside the differential. This would seem a bad thing. The nut/shaft on the opposite side are nice and tight with no leakage. Any idea about what is going on here?