Use great care with vibrating spinners. Get the vibration out. Assure that the spinner turns true. If it does not, believe it or not, you tie the plane down, tie yourself out of reach of the propeller blades, and mark the spinner tip with the engine idling - short of a full balance of the whole thing, it's the only way I know of. Put masking tap around the tip of the spinner, and hold a pencil so as to "tick" the high side of the spinner as it turns.
Check for cracked spinner back plate, and cracks in the spinner around the blade cutouts and fastener holes. I've seen several spinners depart in flight, including my own, because a crack went undetected, and grew during flight. It happens very quickly!