Your going to want to get that seal, 3m make a good contact cement, we also use a contact cement in the production of our range camps, it is avalibale at most cabinet shops. If you can get the panel to pull away from the side at all you will want to pull it away and then place some thing along the edge to keep the separation, spray adhesive on both piece as much as possible and then keep separated for 5 -10 minute. remove whatever you had keeping the pieces apart and press the panels together. Once you have the seperation proplem taken care of then you need to take a piece of sandpaper an scuff up the area around the crack. Go to an auto parts store and pickup a can kitty hair this is a fiberglass resin that has strands of fiberglass, this will help to reinforce the cracked area. Follow the directions on the can. Sand smooth and paint to seal and match. Before you do this repair make sure if possible that you know why the piece cracked in the first place, there maybe something else that has caused the problem. I hope all of this made sense, feel free to contact me if you have any questions.