What I was told when I bought my NSR was the crank seal was gone as the previous owner had let it sit. Supposedly it dries out the crank seal if you don't run them on a regular basis. Can somebody verify?
If the crank seal is gone compression will be lost between the cylinders. Usually the front cylinder runs lean and if you ride it, you'll likely seize it.
It's a possibility that it is a crank seal, but lets not get all doomsday. Compression should be similar for both cylinders if all is right. You should check this with a gauge, not your hands. However, if you can tell a difference by hand, this indicates that it is a big difference.
My recommendation is to do everything else first. Check everything is clean and adjusted, with fresh fuel/plugs etc Check the power valves are operating and there are no air leaks.
After you've done everything, it's time to pull of the barrels and inspect the pistons/rings and test your crank seal.