Hi, welcome to the forums!
I'm very sorry to hear about your T rex. There is a solution where you can tighten joints using superglue. Simply put a little on the joint, then keep moving it until it dries. The result should be a movable joint with added traction.
In practice, this worked for me on unpainted action figures with sturdy plastic, however, I know Schleich uses a lot of paint and rubbery plastic. There is a risk of it causing damage in your situation. I would recommend testing it on a rubbery figure you don't care about first if you want to try this technique.