On my recently purchased Wave Classic, the seatpads and hole covers are loose, need to reattach. What works best? contact cement was recommended. What should I use to clean the old gunk off the hull and back of seatpad to ensure good adhesion but not damage the surface. Any help greatly welcome!

We used 5200 on the hold hatch and contact cement for the pad. This is the most leaky area on the boat.
Rick