chances are you wont need to change the centers... if you do,, you're probably better off finding another crank since they have to be split...
you should be fine just changing the mag & pto side,,, thats where they're gonna leak air... well actually the pto side isnt prone to leaking air since its behind the oil case...
anyways you'll need 3 seals... mag,, pto,,, & oil cover...
heres a way to change them out without pulling the jugs off
http://kawasakitrax.com/kawiforum/index.php?topic=7.0just remember where the shim on the crank goes and dont lose it... you'll see it once you split the bottom end (split the case with the motor upside down & it wont fall out)
and dont use silicone on the case,,, use "yamabond" instead