I was pretty rough with my toys, too. I had the 40th Anniversary box set and a Godzilla vs. Mecha-Ghidorah set. I don't know if Ghidorah's heads were supposed to be removable, or if Mechagodzilla was supposed to split in half at the waist, but mine ended up that way.
MOGUERA's thruster/tail thing came off, too. All I have left of them now are the MOGUERA thruster, and Mechagodzilla's lower half. I remember that a lot of MOGUERA's paint peeled off when I put it in the bathtub, too.
I still have Anguirus, Godzilla, Biollante, Battra, and Spacegodzilla. G and SG are still in good shape, aside from a few chips in their paint. Anguirus is the same way, but his tail also broke off at the base. That's not a big deal, though; I just lean it up against his body, and you can't tell it's not connected. Battra's wings are slightly bent, and Biollante is missing a tentacle.
I also have Shatter-Tail and Combat Claw GINOs, the former of which is somewhere in my attic. And I have the Ultimate GINO, though two shelf dives have left it with a shattered ankle, severed tail, and severed arm. It's in storage; not sure if it'll be fixable.