you should have a metal bracket to hold the RUBBER bush steady and yes the ruber is open so you undo the 2 13mm bolts remove the bracket and rubber will pull off and replace :)
 
its not the bush, between the bush the the metal bar there was a plastic collar. its this which has broken and caused the bushes to be loose, not the metal bracket.
 
im not aware of this plastic collar then as when i had my arb apart i only saw the rubber bush the metal braket and the 2 13mm bolts :think:

it should have a slit to allow you to replace it