The kick lever may be seized due to a large piece being stuck between the crank and the case. Also there may be particles in the bottom end bearings. Opening the case is your best bet, and you shouldn't even attempt it without either a manual or a friend with experience. There are a few special tools, including the flywheel puller, a heat gun, clutch holder, case splitter and press.
If you choose to flush the cases and call it a day, you might get lucky, but to tell you that it is a good idea would be irresponsible.