This has been the case for me as well. If you leave a smoked cob out in the sun for a little bit the shanks should open up a little to get that stem back in. Once you smoke it, the forever stem should fit just right.It has been my experience that genuine Walker Forever stems will always fit a new MM cob. I have had issues moving to a previously used cob, because the hardwood shank changes size based on moisture level. So, as long as you leave it alone, you'll be fine.