NO you dont have to split the cases to replace the "crank seals'. you have to take the stator cover off, and the flywheel after followed by the stator. and on the other side take the Clutch cover off, the main crank drive gear (maybe ohter gears also). But you dont have to split the cases.
That video refers to splitting the cases to replace the crank BEARINGS not the seals. They include the seals in the instructional b/c its a step in the process before taking out the bearings.
But you dont have to if you only need to replace the seals. Which sounds like the case here.
Also the leak from you head pipe is so common on these blasters and its an easy cheap fix.