On the clutch side seal, the seal is MUCH larger than the crankshaft. There is a cylindrical collar that slides over the crank, inside the seal. The two drive gears on the end of the crank slide on top of the collar and the whole assembly is torqued down with the drive gear nut.
If the collar isn't perfectly smooth where it sits on the crankshaft, it can leak transmission fluid by the collar. You scratch you head and curse that engine up on eisde and down the other because you'll put clutch side seals in one right behind the other and "they all just keep leaking!" but if the collar is what's leaking, putting clutch side crank seals in it one right behind the other won't stop the transmission fluid from burning.
You also have to torque that nut down properly... Stick a penny between the drive gears and throw the torque to that nut. If you don't torque it down right it will work the nut loose because the primary drive gear and clutch ring gear are cross cut and the twisting motion of the gears meshing will cause the nut to unscrew and eventually the gear to shoot up into the back of the clutch ring gear tearing the gear all to pieces, putting metal shavings in your transmission fluid, and making a horrible grinding noise.