I found I had to push with a little force from underneath the battery compartment where the touch pad is located to free the bottom edge of the case. The case came away with two loud snaps. At first I thought I'd broken something, but then it appeared that it was just the plastic above the slot loading super drive that was held in very tightly and needed some encouragement.
I found that the ribbon connecting the top part of the case to the logic board wasn't long enough and the connector did have to be disconnected.
The ring at the top which holds the top screw appeared to be underneath the same ring for the speaker and this made it really tricky to remove the fan.
You really have to get the right angle. Persevere as it will come away with some gentle encouragement.
Be sure to transfer the black tape to the new unit or else replace it with electrical tape.