I just read an article about greasing sealed bearings. You carefully pop off the black plastic seal, put grease on top of the bearings and then put the seal back again. Has anyone tried this? When you did it, were the bearings dry? How easy does the plastic seal come out? How easy is it to damage the plastic seal? How do you damage it, rip it? Bend it? What happens if you damage it, what do you use to replace it?