Les,
I have had no more failure to fires even after replacing the recoil spring. I believe that the FTF's in your gun and other guns and my first R9 dissapear after a short break in. I believe the fireing pin and spring and the corresponding mateing surfaces in the slide get broke in.
By the way, I believe the recomended replacement of the recoil spring has been lowered to 100rds.
Congratulations for sticking with it. Sounds like you have a well functioning gun now.
Mike