Turret Lock On

i want to have my turret keep shooting at a target until it has either left the max distance, or been destroyed. here's my script:

 var Look : boolean = false;
 var Target : Transform;
 var damp : float;
 var Projectile : Transform;
 var Shell : Transform;
 var MuzzleFlash : Transform;
 var fireRate : float =  5;
 var Speed : int = 2000;
 var ShellSpeed : int = 500;
 var TurretAudio : AudioClip;
 
 private var nextFire = .5;
 
 function OnTriggerEnter(other : Collider)
 {
  if(other.gameObject.tag == "Enemy")
  {
  Look = true;
  
  Target = other.gameObject.transform;
  } 
 }
 
 function Update()
 {
  if(Look && Target != null)
  {
  var rotate = Quaternion.LookRotation(Target.position - transform.position);
  
  transform.rotation = Quaternion.Slerp(transform.rotation, rotate, Time.deltaTime * damp);
  Shoot();
  }
 }
 
 function Shoot()
 {
  if(Time.time > nextFire)
  {
  nextFire = Time.time + fireRate;
  
  var muzzleflash = Instantiate(MuzzleFlash, transform.Find("Spawn").transform.position, transform.rotation);
  
  var projectile = Instantiate(Projectile, transform.Find("Spawn").transform.position, transform.rotation); 
  projectile.rigidbody.AddForce(transform.forward * Speed); 
  
  var shell = Instantiate(Shell, transform.Find("Spawn_2").transform.position, transform.rotation);
  shell.rigidbody.AddForce(transform.right * ShellSpeed);
  
  audio.PlayOneShot(TurretAudio);
  }
 }
 
 function OnTriggerExit(other: Collider)
 {
  if(other.gameObject.tag == "Enemy")
  {
  Look = false;
  }
 }

NOTE:

i still want the target to be locked on even if another enemy comes into range.