Thanks to Mark for publishing this detailed solution. It works like a charm!
To be honest the side covers were a bit tricky, and the pulling of wire plugs from the DC Controller board was nerve racking. I was sure I was going to pull a wire from the plug instead. I found that by using a needle nose pliers carefully on one side and then the other I was able to get the plug out. Of course my printer is 12-14 years old so no wonder they were stuck.
Cleaning the mirrors did the trick. Thanks Mark!