What do you mean when you say the hammer wont reset? The gun cycles and ejects the round, chambers a new round and then the hammer is still forward? All the way forward or at half cock? I would change the main spring as well as the sear spring regardless of when the previous owner changed the springs. For all you know he could have put lighter springs in it and thus the problems. I would also hose down the lower 1/2 of the gun while you have the MSH out (brake clean).
Sounds like the PO has messed with the gun. Could be he got a little too aggressive with the polishing or messed with a sear angle or the angles on the hammer hooks, thus the hammer not re-setting.
I am assuming you would have mentioned if the gun was doubling, going full auto, or giving you AD's when it had exhibits this problem.
I should also mention a 23lb recoil spring is on the heavy end of the spectrum! I run a 23lb spring in my Commander to help protect the scandium frame and i only run it with full house defense loads.