A friend sent me this question and I figured I'd see if you guys have any suggestions. He's not a dumb, so I've assumed that he's been tightening everything down fully (but will of course suggest that when I report back).

My crank arm keeps working loose on my non-drive train side, I understand that this means there is damage that is causing the taper on the crank and the taper on the bracket to not engage fully and therefore pedaling works the bolt loose, but is it more likely that the damage is on the crank taper or the bracket taper? Its not a sealed cartridge bracket, its the old style with the ball bearings/cups/spindle.