Just a bit of news on this part if you didn't know or something, I'm only doing this when a part breaks or wears out, something in between, so, hopefully don't expect these often.
This part over common use in movement will wear out and loose its friction, making that joint less stable and unable to bear more weight than normal. The rubber in these parts will rub away and decrease friction.
The part on the left is a new Extender joint, while the one on the right is a worn out part.
It is a good idea to stock up on this part if you have mocs that use these and you interact with them frequently, as in Stopmotion and along those lines.