>>9823846After spending some time struggling like my OG Yume again, I swapped out the ball joint that connects her chest with her stomach piece with the one from Lily and it's so much better, it feels like I can actually pose Yume without her falling apart all the time.
Lily on the other hand, managed to fit Yume's balljoint with the seemingly slightly flared peg just fine, took a bit more effort to seat in but nothing too excessive, and she remains stable and posable. Kind of a bummer that this kind of thing has to be done to get a proper fit, but at least my Yume isn't falling apart all day now.