Dismantle Bosco kitchen mixer?

I have a Bosco AS-1200 HD, and one of the beater spindles has dropped out. I'm sure it's a simple repair; the top end of the spindle has a female thread and it appears that a retaining screw has become dislodged. My problem is that I can't see how to remove the top cover to re attach the spindle. I have removed the screws that hold the cover on, but at the top rear of the machine, a vertical shaft passes through the the cover, with a soft moulded gear attached which prevents the cover lifting off. (This shaft drives the blender attachment) I'm hoping someone has experience with this machine, and can advise the next step.