Is it a uniloc quick release? If a quick release, take 2 rubber pads, have someone hold their hand out, you hold the extension with one hand with a rubber pad wrapped around the dia., and have the other pad in your hand ready to grab the shaft, and rap the upper part of the shaft against the other persons hand, like a tuning fork, and as soon as you do that, grab the shaft with the free hand/pad and twist it to unscrew it....most times this will free up the joint due to the vibrations. You may not need the rubber pads, but sometimes our hands cannot grip the parts enough to break it free. If this works, then clean the female and male parts of the joint with alcohol and Q-tips, and a wipe.
Dave