How can I take apart my flymo multi trim 300?

I need to split the cutting head housing on my flymo multitrim 300. I have taken out all the visible screws and released the catch on the rim of the head housing, but it stll seems to be held by someting internal near the roller. Flymo do not appear to have (or want to supply) a manual. Does anyone out there know how to release the two halves of the head housing ?

Brian Barber
April 2009