joint tightening G1's

[Slag]

I usually use superglue ,i think mine is bolt or flash glue, to build up the area that is worn then hit it with a spray of accelerator (OMP insta-set in my case) let it set for a bit then screw the bits back together.
If it's a high stress joint, araldite and steel pins. + grind down the bit thats causing all the issues to begin with (Hardheads chest plate or horri-bulls head,, just ridiculously over-sized tabs)

I should have said. pull the loose area apart first. Most loose joints are just because the plastic has worn down over time and it needs to be built back up.
Most transformers can be pulled apart easily enough. (i've only ever had problems with Blot, He seems to be glued in places) or sometimes you can just roughen up, or put some dents in the surface of the joint, I used to bite the tabs on my lego mens heads if their helmets didn't stay on.