How to have an NPC with multiple parts detect damage

I have an enemy NPC built from several simple game objects (cubes, cylinders, etc.). I have followed a tutorial in making enemies take damage if they're within a certain range, and the code works fine on single objects. I have tried both placing all of the objects into an empty object and having them saved as a prefab, then applying the code to them, but when I play the game and attack the enemy, the health remains unchanged.

Code:

Attack code within Main character: #pragma strict

 var Damage:int = 25;
 var Distance:float;
 var enemyDistance:float = 2;
 
 function Update()
 {
     if(Input.GetButtonDown("Fire1"))
     {
         var hit:RaycastHit;
         
         if(Physics.Raycast (transform.position, transform.TransformDirection(Vector3.forward), hit))
         {
             Distance=hit.distance;
             
             if(Distance<enemyDistance)
             {
                 hit.transform.SendMessage ("ApplyDamage", Damage, SendMessageOptions.DontRequireReceiver);
             }
         }
     }
 }

Damage code within enemy:

 #pragma strict
 
 var enemyHealth:int = 100;
 
 function Update ()
 {
     if (enemyHealth<1)
     {
         Dead();
     }
 }
 
 function ApplyDamage (Damage:int)
 {
     enemyHealth -= Damage;
 }
 
 function Dead()
 {
     Destroy (gameObject);
 }

Although I am relatively new to Unity, as far as I'm aware, this should work. Any help would be greatly appreciated.