If it won't "click" in from, the socket, being too small. Try shaving off a little plastic from the back of the socket so it can go a hair deeper and catch properly on the two shaped pieces (near the front edge) that it "clicks" into.
Or is there some extra plastic, on the two tabs, that stops it from "clicking" in properly? Try comparing the two sockets and also try switching the two ball joints and make sure it's not the "ball".

If you sand the ball it will be hard to do it evenly so you might not have, equal, tension. (hopefully not too late now since this topic was, origonally, posted last night)

 

I haven't done anything yet... It's definitely the socket, not the ball... I tried comparing them, and it looks like 1. it won't go deep enough and 2. the tabs are deformed as well

 

I haven't done anything yet... It's definitely the socket, not the ball... I tried comparing them, and it looks like 1. it won't go deep enough and 2. the tabs are deformed as well

 

All I can suggest is to keep compareing the two sockets and try to shave off, a small amount of plastic at a time, until the ball will fit snug. You can also trim off the bottom of the tabs but then the ball would be sitting higher in the socket if you take to much.
If you have a dremel, with a small round stone, that you could place in the socket to take little bits off, it might be easier than using a knife. If you use a knife, be careful not to shave off, too much, of the socket edges while your cutting inside the socket. (use a tiny stone so you don't hit the tabs and you only hit a small area at a time)

Good luck.

 

All I can suggest is to keep compareing the two sockets and try to shave off, a small amount of plastic at a time, until the ball will fit snug. You can also trim off the bottom of the tabs but then the ball would be sitting higher in the socket if you take to much.
If you have a dremel, with a small round stone, that you could place in the socket to take little bits off, it might be easier than using a knife. If you use a knife, be careful not to shave off, too much, of the socket edges while your cutting inside the socket. (use a tiny stone so you don't hit the tabs and you only hit a small area at a time)

Good luck.