Have you taken the the horn spiral cover of and prised out the centre core
This where I have got stopped also there what looks like a push fit clip arrangement that fits on to the circuit board but I am concerned that if by too much pulling and prising it will snap (Result £250 com2000 unit )
Here are some picture of the similar unit taken out of a 406
unfortunately the Aussiefrog thread
is gone at the moment :-(
Let me know how you get on?