The problem I was having was the hammer would stop at half cock at times. Once I doubled up the sear springs I have never had the same thing happen to me again. This also now goes all the way back to when I bought my CPA in 1998. 
The sear spring at that time was also piano wire and you are indeed correct in that it would move off of the side of sear block at times. 
So a friend of mine cut a groove in the middle of the sear block to stop it from taking place again. 
I then changed it over to the flat spring and when I say backing off of its attachment screw abit. It still has more than enough tension on it to keep it keep it from moving / backing out and then becoming loose.