Thank you MichelArgouet - a brilliant diagram which has help me understand more.
I now know what is causing the misaligned posts but don't know how to cure it. I can push the positive tube up from the bottom so that it is level with the other post. However, when I turn the screw down to secure it the tube goes down also and part of the tube comes out the bottom. As you can see in the pictures:




I still have the second problem in that I cannot push the cap sleeve down but first things first.
Edited on 4/25/2016 at 2:13 PM. Reason: