If the leak is coming out of the top of the cuff it isn't the blade shaft mechanism that's leaking. Double check the gasket or look for cracks in the canister or cuff. If it's leaking through the bottom of the canister onto the drive motor, then it's likely leaking around the shaft. The blade shaft is usually riveted rather than a bolt/nut that can be adjusted and while you may peen it down some more, it won't stop a leak. Leaking around the shaft means the bushings and seal are worn out, and adjusting, even if it is adjustable, won't stop the leaking. If it is serviceable, which I doubt on a forty dollar blender, new bushings and a new seal will fix it.