Worm gear has pulled out, do I need to replace my operator?

I have 2 crank covers that are cracked. I can open the window, but when I try to close it the worm gear comes out and the window stays open. I can close the window by hand. Will a new plastic cover fix this, or do I need a whole new crank assembly? It seems to me all I would need is a cover to keep the gear from backing out, but in one of the threads above you mentioned "that if the worm gear has pulled out, then it is time to replace the operator." Please advise.

Thanks for your help.

Scott