My 597 will not engage the last shot bolt hold open after 3 or so mags fired in succession. I'm thinking that the thin quirky shaped Hold Open Spring (item 15) looses some of its properties when it gets heated. I purchased it used and gave it a good cleaning when I installed a replacement Volq'son hammer (big difference) and both the plastic & metal mags perform the same. Do you think I'm on the right track to replace the spring?