The easiest way to get it off without damage is to apply a little heat to the gear itself.
A heat gun on low is usually enough so you can avoid torching the plastic case.. and then use a small, two-jaw puller.
You can sometimes wiggle it off with a couple of flat-bladed screwdrivers prying evenly if you're gentle, but I think the puller is the safer bet to avoid cracking the gear or bending the crank.
Once that's off, the seal will be right there. Good luck with the repair!
