No one I know of has been able to successfully repair one of these. You'll probably spend hours and hours fooling with it to no avail and risk damage to your machine taking it apart over and over. Bite the bullet and pop for a $50 replacement drive. Here's one: http://www.gainsaver.com/catalog/Detail.aspx?&CCode=2767^Apple+Parts&CCode=2778^iMacs&cICode=126909
You already know how to install it.