Problems rotating back to zero

Hi.

I recently created a script that made the player lean with middle mouse click and drag. The problem that appears, is that the player does not rotate back to zero (on the Z axis). It rotates closer to 0, but still far from it. I get a different number every time.

Here is the script causing this problem (sorry for the length):

 var leaning : boolean = false;
 var maximumLeft : float = -30;
 var maximumRight : float = 30;
 var currRotationZ : float = 0;
 var rotationSpeed : float = -5;
 var backToZeroSpeed : float = 2;
 var smoothDampVelocity : float;
 var maxSpeed : float = 5;
 var mouseLookObj1 : Transform;
 var mouseLookObj2 : Transform;
 
 function Update () {
     if(Input.GetMouseButton(2)){
         leaning = true;
         if(mouseLookObj1){
             mouseLookObj1.GetComponent(MouseLook).enabled = false;
         }
         if(mouseLookObj2){
             mouseLookObj2.GetComponent(MouseLook).enabled = false;
         }
         
         currRotationZ += Input.GetAxis("Mouse X") * rotationSpeed;
         currRotationZ = Mathf.Clamp(currRotationZ, maximumLeft, maximumRight);
         
         transform.localEulerAngles.z = currRotationZ;
     }if(!Input.GetMouseButton(2)){        
         leaning = false;
         if(mouseLookObj1){
             mouseLookObj1.GetComponent(MouseLook).enabled = true;
         }
         if(mouseLookObj2){
             mouseLookObj2.GetComponent(MouseLook).enabled = true;
         }    
     }if(!leaning){
         currRotationZ = Mathf.SmoothDamp(currRotationZ, 0, smoothDampVelocity, backToZeroSpeed);
         transform.rotation.z = Mathf.SmoothDamp(transform.rotation.z, 0, smoothDampVelocity, backToZeroSpeed);
     }
 }

Thanks,

Luka.