The rubber, I don't know what to call it, a gasket? That covers over where the mirror post goes into the handlebar? One of mine has come loose and I can't seem to figure out how to make it fit into the hole tightly. There's a tab and a notch, but it doesn't seem like it's tight at all, so it's just kind of resting there. Is there some trick to making it fit that I'm missing? And is water getting in there anything to worry about?