It is easy to think it is the valves that leak, because if the cylinders leak the air will escape throo the valves. It is the valves that makes that irritating whistel sound[>:] In maybe 95% of the cases it is the cylinders that have the problem. Be aware of that before you changes the valves and hope everything will be fine.
Good luck with your F-16, I'm sure the leaking problem will be sorted out.