I just got done doing this job, to get the seal out I poked a hole in it then used a hooked pick inserted into the hole and pulled it out. When you poke the hole, dont go in to far, there is a land behind it so try not to mar it. the new seal installs easy, just tap into hole till flush with the bore. That seal will always leak when you have the middle gear cover off because it supports the outer end of the shaft.
The seal is in the motor case not the cover. Be sure to lube the shaft where the seal rides Nd the outer end where the cover supports it.