I bought a new sear assembly to upgrade my 2007 model year M&P that I just bought, only to fins that the sear had apparently been upgraded already. But, the new sear assembly I just got has the large hole filled with something that looks like a bearing, whereas my original just has an empty hole. I wonder if it may have something to do with the models that have the thumb safety. The one on top is the new one I just got from Brownell's, the bottom one is one out of my pistol. I removed the Magazine disconnect from both of these.