My fix for a floppy waist on Brawl. Using a single lego plug. Yeah it takes way waist twist when plugged in, but a lot transformers barely have that so no biggie for me. Also just unplug to use waist its not in the way, and also it does not bother the transformation or alt. mode.
welp i finally know what fix i'm using for brawl. Holy shit that is so exceedingly simple! And the best part about it, no modifications to the figure are required! perfect, bravo!
Google directed me here, great work! Went to a lego collector friend, took a knife and some tamiya cement and boom! Only problem is that my brawl stands a bit too upright, but I probably didnt cut enough, still though works great!