I've been dragging my feet to type this up because I hate taking pictures mostly, but I fixed my AT-ST a little while ago after a little experimenting. This, to me, was the best option. It's solid, it's not cheap feeling, it's not going to permanently change your AT-ST at all, it also is virtually invisible, and it won't damage the walker either.
I'm big on NOT altering a toy in my collection permanently without having a 2nd unaltered one. I wasn't buying a 2nd AT-ST just so I could make one stand by damaging it through glue or something, so I wanted a fix I could just pop off as easily as I put it together, and this was it.
All you really need is a (small) phillips screwdriver most people probably have and a couple 5/16 internal washers, and a little spike of metal (sewing needle or whatever, something thin, I used a scribe like a little dental pick). The washers can be had at any hardware store, or I'd imagine Wal-Mart even. I got mine out of just my random assortments of stuff like that I keep around.K-Mart Vintage AT-ST Wobbly Ankle Joint Fix Tutorial!
Click, fix, enjoy.
If any of it is confusing drop me a note in here and I'll attempt clarifying it as soon as I'm on which is varying a lot these days, but this is honestly pretty straight forward stuff.
My walker looks like a beast standing now high above my Endor figures.
Can't wait to add some figures to it too (which it now actually can hold them without collapsing).
I only had one joint I'm having a big issue with, just as a note. Everyone seemed to have a problem with the one joint, not the others, though overall I'd say this walker is generally less stable than the previous versions. Mine's a LOT better after this fix, but I wouldn't say it's perfect. My Attack On Hoth and Wal-Mart AT-ST's are all a little tipsy though if bumped hard enough, and so is my Endor Vintage AT-ST now, but it's as sturdy as my Attack on Hoth one I'd say, if not more so.