Thanks for the nice comments everyone.
I took the front 'beam' off whilst I had the front bumper off, although I think there is a guide somewhere on here which explains how you do it with the bumper on.
The unit is sealed heavily with a white glue/sealant so I gently prised it apart. Take your time. Then all the bits inside just slot together and are held in with small screws (with a star shaped head I think - possibly T12). I undid all the screws, removed and then cleaned the components and then sprayed them matt black. I did back and front. There was also 2 coffee coloured pieces of plastic in the unit which I chose not to put back because they weren't black.
The logo'd area was black anyway, with a silver H, so I masked it up, and then gave it a quick polish before refitting.
I then added clear sealant all around the seal (although there was plenty of the old stuff in place) and fixed the unit together. I put a brick in a cloth and weighted it down for 20mins to help the seal.
Then just popped it back on.
It all makes perfect sense as I write this, but feel free to ask if you have more questions.