I'm sorry for the trouble, @El Frazoo, but glad you found the problem.
I doubt your hub rounded out on the pothole where my suspension broke, but the roads and the way we drive on them surely contributed to both equipment failures. We're pushing well past the design parameters (assuming there were any) for aftermarket VW parts, which in most cases don't even approach the quality of OEM parts in a German economy car last built a half-century ago.
Tearing through the mountains at twice the posted speed limit was never what the Sainted German Engineers imagined, and the suspension and brake parts were never designed for how we use them. The absolute weakest of weak links is how the rear hubs are fastened to the car. It's a perfectly fine setup for profiling, and comically inadequate for how we use them.
Tom Boney had a similar failure in his IM on the same roads a few years back. I've actually torn the friction-welded center out of a CB rear hub several times channeling my inner hick-town, white-trash hooligan. The next setup on the car will be a CSP (I'd do an AirKewld, but the Euro is in the toilet, and Pete's pricing has gone nuts).
Suffice it to say, I feel your pain. The ultimate fix is to spend the long money to try to ensure it doesn't happen again, and to check the tightness of the castle-nuts frequently. When you think about what is actually happening, you can understand why this nut being really, really tight is the only thing standing between you and a pretty catastrophic failure.
The advice Gordon and Al give regarding the torque of the castle nut is good, but I've learned (out here by myself) that 217 lb ft or 250 lb ft (or whatever) is the barest minimum. You do you, but I'm torquing that particular nut as tight as I can get it. The chances of stripping it are near zero, and the downside of it being too loose is exceedingly bad. I go to at least 400 lb ft, but I'm a spot-torque man on this particular piece (torque it until you see spots). In this instance, I'd tighten with a breaker bar and cheater, and just check it with a torque wrench set to 300 lb ft. I just want the wrench not to click.
Other, better, more careful professional mechanics will be aghast at my ham-handed approach, but it's worked for me, and I'm a lowland gorilla who drives like his scalp is on fire.