Look in the back of the cylinder and make sure it has the groove machined in the hole for the new rubber band.
And like others said, getting the old pushrod out is a pain. It may be easiest if you pull it from under the dash while the MC is still bolted to the firewall. Maybe not.
I have also grabbed the whole thing in a vise, and yanked on the pushrod and pulled the whole guts out of MCs before. It can take a lot of yanking to get the old one loose.
