Scrolling Texture scrolls both maps. Only want single map to scroll?

Hello, I have a script to scroll my texture but in my material i have a main texture with transparency and a separate texture as an independent greyscale alpha. However, it is scrolling both textures together and I don't want that.

I want my main texture to scroll and appear to fade at the top. but the fade I have made scrolls with the main texture.

 var ySpeed : float;
 var xSpeed : float;
 
 function LateUpdate () 
 {
     var offset = Time.time * ySpeed;
     var offset2 = Time.time * xSpeed;
     renderer.material.SetTextureOffset ("_MainTex",Vector2(offset2, -offset));
 }