Have a 2002 496 mag. The port side air actuator drain system opens at 3000rpms and higher filling the bilge with water. Pull up on the release valve and the system closes for a few seconds, but then reopens. Any ideas or help?

They just go bad after a while; it's happened to many of them. It needs replaced. You can rebuild them, but your money and efforts are better spent just replacing it.

www.bammarine.com
www.dolleroffshore.com

Either can get you the part. It only takes about 30 minutes to replace if you can get to it, and you have a good set of (normal) tools.