Common faults:
Brushroll motor
Brushroll PCB
Ends of the brushroll wear causing noises and jumpiness
The outer plastics get battered
The little white ball-motor housing bush wears down, sometimes completely away
The main motor burns out
the main motor sparks like a bastard
The middle bin release rod part, (that sits behind the 2 halves of the upper cyclone) has a spring that needs to be at the right orientation to work (needs to push the release rod back and past the bin when fitted) is AN ARSE.
The spinal cord is very tricky to get out, and at one point does need a scary amount of persuasion to be removed
The post motor filter catch can be a bastard, if it pops out it jams the ball which is gr9 fun to rotate it to where it needs to be to get at the filter...
Still better than a dc50 though, at least parts are cheaper for a 24...