I tried to repair one once. Full of admiration for the design as I took it apart with some head scratching. Considerably more head scratching when I couldn't find anything wrong so sprayed the motor with WD40 and put it back together.
Switched it on and bingo! it worked.......next, the WD40 caught fire, and I ended up with a multi coloured lump of plastic that was once a Dyson.
Replaced the motor in our dc07 couple weeks back, easy job and cheap enough (£18 new motor, delivered!), see how long it lasts . Suprising thing even worked when I got it back together.