Why My Gun Rotate When i keep on pressing my mouse button and Move the Mouse

Hi There...!!! I have a First person Player which has a camera and Gun is the child of that First person's camera. The player and gun is working properly. The problem im facing is that,when i Click the left mouse button and Move the Mouse,And then stop movement of My mouse,logically my Gun should also stop moving,but it starts rotating around its origin? and keep on rotating untill i release my Left mouse button. Script is as below:

var clickPos : Vector2; var offsetPos : Vector2; var divider = 80;

function Start() { clickPos = Vector2(0,0); offsetPos = Vector2(0,0); }

function Update () {

 offsetPos = Vector2(0,0);
 
 if(Input.GetKeyDown(leftClick()))
 {
     clickPos = mouseXY();
 }
 
 if(Input.GetKey(leftClick()))
 {
     offsetPos = clickPos - mouseXY();
 }
 
 
 transform.Rotate(Vector3(-(offsetPos.y/divider),offsetPos.x/divider,0.0), Space.World);

}

// Prints the current mouse position function OnGUI () { /*GUI.Label(Rect(10,350,200,100), "mouse X = " + Input.mousePosition.x); GUI.Label(Rect(10,370,200,100), "mouse Y = " + Input.mousePosition.y);

 GUI.Label(Rect(120,350,200,100), "click X = " + clickPos.x);
 GUI.Label(Rect(120,370,200,100), "click Y = " + clickPos.y);
 
 GUI.Label(Rect(210,350,200,100), "offset X = " + offsetPos.x);
 GUI.Label(Rect(210,370,200,100), "offset Y = " + offsetPos.y);*/

}

//////////////////////////////////////////////

// Return true when left mouse is clicked or hold function leftClick() { return KeyCode.Mouse0; }

//Immediate location of the mouse function mouseXY() { return Vector2(Input.mousePosition.x, Input.mousePosition.y); }

//Immediate location of the mouse's X coordinate function mouseX() { return Input.mousePosition.x; }

//Immediate location of the mouse's Y coordinate function mouseY() { return Input.mousePosition.y; }