Thanks for all the advice. In this case, I took the advice given to me by my neighbor (he's a bmw motorcycle mechanic): Get a sharp punch, and lightly hammer the tip through the flat part until you go through the metal material of the seal. Then do it again on another part of the seal (I did it at 12 and 6 o'clock positions). Once you get through that, it's easy to grab the seal with the tip of the punch and work it out, alternating from the top and bottom parts. If that doesn't work, drive (shallow) a small screw into the holes and then grab the heads of the screws with a pair of plyers.