who ever made the GXP that manufacturer may have info. . GoGo inspector Gadget ... google away ..

the hollow tube suggests you remove the left arm then pull the whole right end of the crank and the spindle it is fixed to

out thru the bearings ..

have never seen that combination in the flesh , so since its a hubrid , I suspect the tube spindle is splined on the left end ..

is there a crank arm extractor thread inside the left crankarm to pull it off the splines ? do you have the right extractor tool already?

Id really have to be there to see enough . Try Your LBS?