You're either not getting them all the way back in or they have shrunk (which is normal)... or some combination. Yes, they can be replaced. Or, you can slice the rubber in a low spot along the bottom edge to take the stress off the corner. You can fill the gap, if you want, with something like black LifeCalk if it bother you. You could also try, if you wanted, using some LifeCalk to help keep the rubber in place, before cutting it.