There were 2 types of dc07 cyclone units.
I think there were problems with the early ones and it may have been to do with with those black bits. I've read threads that said cyclone units had to be 'de-rooted' even though they are called root cyclone.
The early one clogged and the whole top section of a cyclone unit would be rammed with dust and hair. You can see pics online. My aunties dc07 clogged up like that but that was because she never used to knock the top of the cyclone unit when she emptied it, instead just dump the stuff from the bin and close the flap again.
Its good in general to give them a blast out. If you can stand the dust cloud
DC01, DC02, DC03, DC04, DC05, DC07 + USA DC07, DC11, DC15, DC16, DC17, DC18, DC24, DC25, DC26, DC27, DC41, CYCLON !!