Step 11: Duplicate the grunge layer, flip it horizontally and set the blend mode to "color dodge". You may want to darken the bottom edge of this layer as well... paint it, burn it, whatever floats your boat.
Step 12: Open up your original metal texture. If necessary, flatten the layers. On the layer above it, put whatever image/texture you'd like to have on the texture. I'm just using a dingbat. Set the layer to "overlay" and decrease the layer opacity to about 85%
Step 13: Duplicate the image layer and set it to invisible. On the original (the bottom layer), do a motion blur at a 90 degree angle. Rotate the image 90 degrees counter clockwise. Go to filter -> stylize -> wind. I do the wind one. Run it twice. I did a stagger the second time
Step 14: Rotate it back 90 degrees clockwise and turn the top layer back on. Line them up with one another if you have to. You'll probably barely be able to see the "wind" layer so adjust the brightest and contrast as necessary. I also set the layer mode to color burn and reduce the opacity to around 20%
Step 15: Underneath both of these layers, create a new one. Select a nice rusty color. Randomly splotch a few places at the bottom edges of your decal. Set this layer to "overlay" and reduce the opacity to about 65%. With a grungey shaped smudge tool, click on each of your rust splotches and drag downwards to create a streak. Do this all the way around and adjust as you like. It also nice to smudge a little on the decal layer and the "wind" layer. Tack on the other effects if you want
This is a texture I created using several of the afore mentioned techniques. Just to kinda show what you can do with it...