I agree that in order for the volume buttons to work properly, the rightmost and middle screws that hold the volume button bracket should stay a bit loose.
For those having a problem reseating the mute button assembly, remember to put the mute button in the right orientation: silent towards the rear glass, normal towards the LCD, then hold the phone horizontally and reseat the rest of the assembly then the bracket, using a spudger. Remain patient, do not use excessive force, this is the key to avoid tearing the sensitive flex cable.
Martin, you can and need to remove the headphone jack in order to remove the topmost screw. You can do that with a pair of tweezers, there are no screws holding the jack, probably only some glue beneath.
I agree with onepilotairforce, you have to remove the headphone jack in order to remove the topmost screw