Fortunately it was a cheap wheel - unbranded Formula hubs and Alex DA14 rims.

How can I fix this? I cross-threaded it pretty badly; I can't get the lock ring out. Anyone use Loctite's make-a-thread compound? What about Loctite red once I get it out? I'm thinking that the Loctite red might be useful if I get the lockring out and there are still some usable threads left.

If anything I can just get a new hub and relace the rim since I now have a truing stand - would be a good learning experience, building my first wheel!

Also, is it just me, but are cassette lockrings pretty easy to cross-thread? This is my second time ... and I just learned about the "trick" of spinning whatever you're trying to thread in the direction that loosens it until you hear a click or feel a clunk . Fortunately the first time I cross threaded a lockring I managed to get it back down evenly without too much of a hassle. Hoping it's the same deal here ... Once I get the locking out.

One reason to consider the plastic lockrings. I just ruined a DA freehub by paying more attention to the torque wrench than the lockring. Makes me
want to get a 3/8" torque wrench as the 1/2" one has a 13" lever arm. To remove you just need a longer lever arm. Don't depend on loctite to
salvage your threads, the cassette will be loose and may not even clear the hub axle depending on how buggered the threads are, but sounds like
they are pretty toasty if you "can't get the lockring off".

Use a chainwhip to keep the cassette and freehub from turning. Use the quick release to hold the locking tool in place so that it won't pop loose. Then back the locking out using on open end wrench or crescent wrench. If you can't fix the threads check with the hub manufacturer to see if the freebie can be replaced. A Shimano freehub might work.

Where can I get plastic lockrings? Those sound pretty awesome.

You could try replacing the freehub on the hub itself with a new one.

I must say that I have never botched a cassette lockring, or a fixed gear one either. Part of your education is that aluminium threads are really delicate if you want to screw a threaded piece of steel anything on to them. Check and double check that click technique, and if after the first 1/8th turn you feel resistance, stop, unscrew and try again.

Well, the cassette body is steel, I verified with a magnet.

The threads were also undamaged. When I tore off the lockring with a giant 18 inch wrench, I looked at the threads on both the lockring and the cassette body. Looked surprisingly good for something that was cross-threaded. A little bit of dirt, I wiped that away and applied some marine grease and tried tightening on the lockring using my fingers first only before I busted out the wrench.

Of course, the wobble in the whole cassette was still there - symptomatic of something not right.

For a while I actually thought the smallest cog was BENT. I had, after all, put it in the dishwasher and dried it in there too. I couldn't help but wonder if the high heat might have slightly warped the cog. It wasn't LEVEL on the rest of the cogs.

I quickly dispelled that thought when I took off the cog and put it on a level surface and found that it lined up perfectly on the surface.

I then realized my mistake - I didn't properly align the teeth of the sprockets on the cassette body!! Wow! What a dumb mistake!

I aligned all the teeth this time and tightened down the lockring using finger pressure only and what do you know! No more cassette wobble! I then pulled out the wrench to get to 40 N*m or whereabouts!

Practicce makes perfect. And so long as the mistakes aren't expensive, you do learn by them!

Good job! I think I made that mistake sometime in the past.

Shimano, for a time was supplying plastic lockrings with certain levels of cassette in the 8-9 spd heyday. None of my recent cassette buys have had them
so they may have been a passing fad. I never used them after I realized they were plated plastic and just recycled metal ones as needed.