As others have indicated the fence is plywood with laminate over it. You need to peel the laminate off which is not easy but you need to do this so you can access the screws that attach the fence to the tube. Don't throw the fence away because you need to use it as a template. Once the fence is off you can check to see if your tube is flat or not. If the tube is out you can mark the areas where you will need to shim it.
You can use the old fence as a template for the screw holes so the new fence will fit. The screws are recessed in the fence so by using Corian you will have the holes showing but are high enough not to be an issue. You then shim the fence flat.
Before you take apart the fence have you tried to adjust your fence to get rid of the dip? If you have a dip in the middle of the fence you may need to shim it but if its on one of the ends adjusting the fence can help. I have a slight dip in the middle of my fence but the boards come out fine. I set it at 5 inches and they come out 5 inches.