TalkBass Forums - Missing Truss Rod Nut...

So, about two months ago I bought a used '06 MIM P-bass off of craigslist for $185. The price was good, I asked the guy if anything was wrong and he said no. I tried it out and it worked fine. The pickup poles were covered with rust, the frets were kinda discolored, and there were some decent scratches on the body, so I figured that the price was fair.

Anyway, I didn't really play it until Christmas, when I technically received it as a "subsidized" present. I slapped on some GHS Precision Flats, but when I went to adjust the truss rod to compensate for the tension, it appeared that the nut is missing. The TR is unbroken so it should be a repairable issue, correct?

So pretty much, I have two questions:
1) What size nut would this P-bass need?
2) Is this an easy enough to do myself? The only experience with a luthier in my town is reading some sketchy ads on CL, and the next closest one that I trust and have been to in the past is almost half an hour away. I would prefer to DIY, but I could always go to them if I needed to.