I just stumbled on Fastbolt’s detailed answer to a fellow member who was having the exact same problem with their CS9. Dated 8-16-14, 9:31 pm.
One point that really caught my eye was his practice of replacing those flat CS9/45 recoil springs even more frequently: 2-3 years or 800-1200 rounds +/-. That plus 18DAIs post above have me thinking...at about $4 per spring, why not replace it every 2-3 years.
There was a bunch of other good info in his post and that thread as well.