I guess I should have tried harder.
I went to the dealer and in 5 seconds he had unlocked the lock and removed the cover.
Following his demonstration I tried it and wallah, the cover was removed.
For you new owners of the G5 here is the trick to getting your air filter box lid unlocked.
1. With the key in the lock, place your thumb right under it on the cover.
2. Push in hard and you should see the cover move slightly inward.
3. Turn the key counterclockwise.
There is a rubber spacer on the body of the lock located between the cover and the frames metal tab. This spacer must be compressed before the lock's catch can turn so pushing on the cover below the lock will free things up.
Thanks to all of you for your help and, if he is reading this, thanks to my dealer for teaching me how to do this.