Thumbs up for this tip. I left it out in the sun for 15 min only and it worked a treat. I used a razor blade. The plastic tools are next to useless.

Yep, I had exactly the same problem. The alignment was way off.

The clip has a hole and a groove. This is good enough to grab it with some pin tweezers from the top when replacing it.

Yes, this is hard. It would be a lot easier if the guide had a picture of the retainer clip. I was successful with a spludger by lifting it on the upper left hand corner. Once you have it off, have a good look at it before putting it back on. Remember that it clips to the outside of the camera housing.