Cases do not have to be split to replace a crank seal. It's very simple to replace the crank seals. Remove clutch cover, then take off the 5 springs and nuts for the clutch plate, remove the cluch boss nut, then remove the thing that holds the disks , followed by the clutch basket, next remove the gears that are on the crank itself, take off seal retainer, Take out old seal put in new seal, reassemble. Make sure you line up the marks on the balancer gear and the crank gear. Also line up the 2 dots on the clutch basket and the plate the springs go on. You'll understand once you get it apart.
Good luck I hope this helped.
BUT before you pull this all apart does it smoke very badly. Very heavy white smoke will pour out if your crank seal is bad.