http://www.amazon.com/Lisle-56750-Seal-Puller/dp/B0002SRCKG

Will that seal puller work with the transmission countershaft still in place?

Not sure how that sprocket mounts, but it doesn't have the single large nut most bikes do.

The OP will have to remove 2 small bolts and the sprocket retainer bolted to the countershaft sprocket to get it off.