Neck is Back Bowed... HELP!

[erosier]

Hi,
My Kawai RB865A Bass is back bowed to the point where I read the Stew-Mac Set Up and a few others and figured out I needed to loosen the truss rod. So I loosened the strings and when I got in there the nut was loose. So loose that there was no resistance to turn it left and it only took a few left turns for it to come completely off. I took the neck off the bass and found there's no other way to get to the truss rod so my question is, am I screwed and need some serious work done or is there another way to fix this?

(I got the bass off of craigslist and there were other problems with it when I got it).

Thanks for the help,
Eric