I just had mine apart to replace the o-ring so the locks do not freeze up any more.

There is a little roll pin that attaches the long shaft with a flat on the end which turns the lock mechanism.

To reinstall the door lock cylinder, put the key in the cylinder to be sure all the tabs are pulled in, then put the o-ring on and insert the lock into the handle. Then from the back side, there is a torsion spring that needs to be wound and put in place.

Once that is done the long shaft with the flat on the end fits over the tab on the end of the lock and a small roll pin is driven into the shaft and through the lock, which keeps the cylinder from pulling out.