MacBook Core Duo Fan
When I took the old fan out I saw significant build-up of dust on the left side (as seen in the pic of step 18. Blew it all out, cleaned up the heat sink and all other dust. BUT when I went to replace the 6 mm screw on the left, it would not seat into its threads. I had to take out the fan again to find out what was wrong: The threads had come loose from their housing, a plastic housing holding brass threads. The plastic had cracked and released the brass threads. I guess the overheating on that side due to the excess dust had caused it. Anyway, nothing to do but to clean out the pieces of plastic and remove the brass threads so it wouldn't rattle around inside the computer. I just left out the 6 mm screw and hoped that the one on the right and the 11 mm screw from step 5 would hold it well enough. So far seems to be good.
BTW, it was impossible to get the old fan out without tearing the black felt tape. I put it back as best as I could and sealed the tears with a piece of paper tape (first aid-type) (assuming that it should be non-conducting).