Bone rotation during animation?

Hey guys, after about an hour of trawling the forums/answers I can’t find a reliable solution. Here are the details:

The problem:

My player is able to aim up,down,left and right with no problem whatsoever and I have successfully rotated the bone with no problem. However, if any animation is playing, the bone will refuse to rotate. I have tried implementing the rotation function into FixedUpdate() but that just snaps it back to the animation after 1 frame.

What I want:

I would like to know how I could achieve the effect of controlling, a potentially, animated bone during an animation. So I want to override the original bone animation with script. Is this possible?

My script for the sake of it:

var spine : Transform;
var rotateSpeed : int = 18;
var pos : Quaternion;

function Start()
{
	animation["Idle"].layer = 1;     
	animation["Idle"].AddMixingTransform(spine);
}

function Update()
{
	if (spine.transform.rotation.eulerAngles.z > 294)
	{
		Debug.Log("294");
		spine.transform.rotation.eulerAngles.z = 294;
	}
	
	if (spine.transform.rotation.eulerAngles.z < 244)
	{
		Debug.Log("244");
		spine.transform.rotation.eulerAngles.z = 244;
	}
	
	if (gunAiming.aimMode == 0)
	{
	 spine.transform.rotation = pos;
	}	
}

function LateUpdate()
{
	if (gunAiming.aimMode == 1)
	{
		spine.transform.Rotate(Vector3(0, 0, Input.GetAxis("Mouse Y")) * Time.deltaTime * rotateSpeed);
	}
}

Please just ask if you need any more information, and please do not tell me any script, I like to learn not implement.

So, the answer:
What’s happening in this Script? Lets concentrate only on rotation values of bone wich we are trying to rotate.

Frame 1: Animator set rotation r1 to bone;
Then we rotate bone with value x in LateUpdate();
Result: r1 + x.

Frame 2: Animator set rotation r2 to bone;
Then we rotate bone with value x in LateUpdate();
Result: r2 + x.

So, as you can see the rotation value in current frame value is independent from the rotation value in previous frame. So thats why you havent progressive rotation, in fact we have the constant rotation offset in this script.