Originally Posted by Greg Bender
IIRC, it pops out the top. Can be removed using typical "dental pick" tools. Just be careful not to gouge anything and you'll be set. Pretty easy, actually.
"Dig" it out from the top. Just make sure you get everything out and the hole is nice and clean before you try putting the new one in or it won't go. A little oil in the hole and on the new seal will help it slide in.