I have an old sylvan gunite pool in a house I just bought and it looks like the slab that the skimmer is in heaved and cracked the skimmer. The flapper door is gone as well. How would I figure out the correct one to replace it with. Would it be better to remove the old one before ordering the new one? I would like to pressure test the lines first but I dot want to pay someone to come do it. Any tips for doing tht myself would be awesome