I purchased a 2.0 Clawdeen recently that had really loose knees and the nail polish method worked well for me. It took several coats, allowing each to dry completely before reapplying to prevent it from gooping up. I've also used clear nail polish to tighten loose arm connections on the older dolls that lack the ball-points to keep the pegs in place. I don't know if different brands will have different results, but I use Sally Hansen, Hard as Nails Xtreme Wear, Invisible. Typically, you should just be able to pick it off the hard plastic with your nails once it's dried if it's not working out, so no harm no foul.
Good luck!
The FabriTac may also be a good plan for something a little more permanent, it's really durable stuff. I may have to try that myself if the nail polish begins to wear out.