Assuming it's square taper, it sounds like it was under tightened, and has rounded off over time. Solution is to replace the crank arm.
Take it to your local bike shop to be sure.
@mattty started
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Assuming it's square taper, it sounds like it was under tightened, and has rounded off over time. Solution is to replace the crank arm.
Take it to your local bike shop to be sure.