First off, welcome to WWN.
You seem to have quite the number of issues with your CPS 2500. It would have been a good idea to consolidate your questions into a single thread rather than addressing each minor issue in separate threads.
The pics are a great help though. The rubber gasket on your pump has probably shrunk like many others do, you can try and add something underneath the flange to improve the seal. I've used vinyl tubing, and marauder has used o rings.