You think some WD40 might clear things up? :P
nonononononono. not sure if you were joking but WD-40 is srs bsns. No WD40 on bikes
ever. a) it's not a lubricant and b) it'll fuck up any lubricant that's in there. Internally geared hubs with internal brakes are especially dependent on proper lubrication, because the gearing requires lots of oil while the brake requires high-temp grease, then all the seals and bearings require waterproof grease on top of that.
I did some more digging for you. Here's
Sheldon's page on Nexus hubs with more links at the bottom of the page,
a page with step-by-step photos of the disassembly and lubrication process, and
another page that doesn't seem to have much point beside pointing out design flaws, but it has lots of pictures and might help you understand the inner workings.
If I were you and was sure that the problem was inside the hub, first thing I'd do would be take it apart and see if there was a simple mechanical fix. Then try lubricant baths to loosen everything up. Maybe ask your local bike shop if you can use their parts cleaner for five bucks or a six-pack first. If nothing works then, and you're sure the internal mechanism needs replaced, try and fix that before buying a new one. I mean, it's toast anyway, so why not give it a shot? From the tech docs it looks like the whole thing is held together by a couple E-clips which should come off and on pretty easily.