Firstly, I would suggest not flying with a loose rear arm, as there may be an increased risk of further failure while flying. I say this having a bad experience with my M2 after I slipped on icy steps and threw the most expensive item I was carrying. Only hidden damage so I flew anyway, and it fell out of the sky with a failed front arm causing more damage. I replaced front and rear arms myself (I was a Navy ET years ago, so much experience soldering etc).
Rear arm pivot is a black plastic bushing mounted in the lower shell, (mine was trashed but the shell was fine). The spring loaded inside hinge was also damaged as well as the plastic arm shaft - none of this damage was visible, but the arm was loose!
After a crash, you should recalibrate everything, gimbal, IMU, compass, collision avoidance cameras etc, using DJIGO4 with your computer. I'm thinking that may level your gimbal.