Paul is Correct…
You gotta remove the rear cover and then remove a bunch of little square tabs (approx 8+) which then stops the rear part (hicas part) of the pump from working, then all you need to do is plug the hole for the rear line.
If you simply tried to plug the rear hole and not remove the inner tabs then that could be why the seals went… pressure was building up and had no where to go so blew the seal ? ? ?