Problems with Gropuing after a scaling matrix modification....

Well basically the problem is that when a texture(in my case "needle") is suposed to rotate around the gropus center (wich is the resolution of the background image (in my case "speedo") will have an incorrect pivot position...

This would normally not happen, but since I have a scaling matrix modification, the groups are not working properly...

Heres the code:

 using UnityEngine;
 using System.Collections;
 
 public class HUD : MonoBehaviour {
     
     public Texture2D speedo;
     public Texture2D needle;
     
     // Internal    
     private Vector2 currentResolution;
     private Vector2 nativeResolution;
     private Vector3 nativeScale;
     private float aspectRatio;
     private float nativeRes = 720;
     
     private float rotAngle = 0;    
     Rect speedoRect;
     Vector2 speedoPivot;
     
     void OnGUI ()
     {        
         InitGUIMatrix();        
         
         if(speedo)
         {
             GUI.BeginGroup(new Rect(100,0,512,512)); // <---- Matrix gets messed up
             GUI.DrawTexture(new Rect(0,0,speedo.width,speedo.height),speedo); // Background
             Matrix4x4 prevMat = GUI.matrix;    
             pivotPoint = new Vector2(speedo.width/2, speedo.height/2);    // Correct.
             pivotPoint.x /= (screenRect.width)/(Screen.width);            // Needs a modifyer after gropued?
             pivotPoint.y /= (screenRect.height)/(Screen.height);        // ...
             GUIUtility.RotateAroundPivot(rotAngle, pivotPoint); // <---- Fix me...
             
             rotAngle -= 100f*Time.deltaTime; // test rotation
             if(needle)
             {
                 GUI.DrawTexture(new Rect(0,0,speedo.width,speedo.height),needle); // Needle (rotating tex)
             }
             GUI.EndGroup();
             GUI.matrix = prevMat;
         }
     }
     
     /// Inits the GUI matrix.
     void InitGUIMatrix()
     {
         aspectRatio = GetScreenAspectRatio();
         currentResolution = new Vector2(Screen.width,Screen.height); // Just store
         nativeResolution.x = (nativeRes*aspectRatio);
         nativeResolution.y = nativeRes;
         nativeScale.x = Screen.width / nativeResolution.x;
         nativeScale.y = Screen.height / nativeResolution.y;
         nativeScale.z = 1;        
         scaledMat = Matrix4x4.TRS (Vector3.zero, Quaternion.identity, nativeScale);
         GUI.matrix = scaledMat;
     }    
     
     float GetScreenAspectRatio()
     {
         return (Screen.width*(1.0f/Screen.height));
     }    
 }

Heres the original post for the media.