I have been having a problem lately with noise from my crankset and bottom bracket. The noise subsided for a while after cleaning, regreasing, and repacking the bottom bracket, but has resurfaced. It will creak and crank when I climb or ride out of the saddle or when I apply decent pressure on the left crank arm to stop or to adjust while trackstanding. If I grab the left arm and move it, I can feel the slightest amount of play in either the bottom bracket or the crank arm. Other than this, the bottom bracket is tight and there is no noticeable play.

What I need is a diagnosis. I know this is likely to either be a worn taper on the bb spindle or worn taper inside of the crank arms, but I don't know which. I would like to keep the cranks if I can, but if I buy a new bb specifically for those cranks, and then find out that they were the problem, I may not be able to find another crankset that will give me the correct chainline, hence forcing me to get another new bb.

Should I just replace the whole drivetrain? Has anyone had this problem before, and if so, what did they do?
Thanks