Renaming issue for a waypoint system

Hello- I've been working on a waypoint system and have run into some trouble. The script should move unit to waypoint, which is then destroyed and waypoint2 is turned into waypoint, and the process is then repeated. However, while it reaches waypoint fine, waypoint2 will not turn into waypoint- it simply stops moving at waypoint. Any ideas as to why this is happening? Many thanks for any light you can shed on this!

 var unit: GameObject;
 var waypoint: GameObject;
 var waypoint2: GameObject;
 var duration: float;
 var collision: Collision;
 private var starttime: float;
 
 function start(){
 //sets start time for comparison on motion
 starttime = Time.time;
 }
 
 function Update () {
 //detects for the presence of a waypoint
 if (GameObject.Find("waypoint") != null){
 //if a waypoint is present, move it to its location over the given duration
 var startpos: Vector3 = unit.transform.position;
 var endpos: Vector3 = waypoint.transform.position;
 transform.position = Vector3.Lerp(startpos, endpos, (Time.time - starttime)/duration);
 }
 }
 function OnCollisionEnter(collision : Collision)
     {
 //when the unit collides with the waypoint, destroy it
     if(collision.collider.gameObject.name == "waypoint")
         {
         Destroy(waypoint.gameObject);
         waypoint2.name = "waypoint";
         waypoint = waypoint2;
         starttime = Time.time;
         }
     }

Oh, and another thing (although I'm probably not quite thinking clearly right now, it seems like it should be pretty simple, although I for some reason can't think it through...)- does anyone have any ideas as to how to make this unit-specific? Meaning that when a unit is 'selected' the waypoints (placed in gameplay) are applied to that unit in particular, since I'm going to be dealing with a bunch of them... Any ideas? Thanks!