In addition, it is impossible for dried out grease to lock-up the clutch.
Look at the 3D animations in this thread and you will see how the clutch works.
Consider the amount of torque that is being applied to the internal components shown in the exploded view. Dried grease would be no match for the torque at the rear wheel that is transferred through the countershaft.
On some engines the clutch friction material is a bit gummy and sticky as opposed to the typical hard dry friction material. From the time the engine is assembled, until the end-user installs it...it could be months. Months of sitting there with heavy spring pressure compressing the gummy friction material.
This will cause the friction material to stick to both the pressure plate and the inner hub.
It is very rare that it is necessary to free-up the inner hub in order to get the bike to roll. Simply remove the cover, pull the clutch lever, and pop the pressure plate loose with a flat tip screwdriver.
Now...If you really want to make a BIG difference in your clutch...remove the friction pieces and trim them slightly along the edges so that they float in the gear...not a light press fit. This will give you a positive engagement at both the inner hub and the pressure plate effectively doubling your useable clutch friction surface. This is how the clutch was designed and was intended to work. On most of these engines the friction material is just crammed into the gear.
Try it on your next build KC...you'll like it! Hint...prior to doing the screwdriver thing in order to free up the dried grease...remove the friction material from the gear first. You will then find that the hub with the three pins spins completely free...dried grease and all.
Again...refer to the animations...the clutch is incredibly simple.