Probably not the most exciting post, but something that's been annoying me for a while, and finally today I found the answer, so I thought I'd post it.
We've had a cordless Dyson for a while, and since our black lab Nelson joined us, the Dyson has been pushed in to more regular service and generally had a harder life. Having ladies with long hair in the house means that the spinning attachments need regular service.
The motorhead attachment is quite easy to clean, with just a coin and pair of scissors for normal clogging. However the only place that's difficult to remove blockages/hair is the motor itself. I'd stripped it down before by taking about the 8 or so hex screws, but still couldn't remove the part connected to the motor (not sure of it's official name)
However after finally tracking down a YouTube video from Mark Chalmers which shows there's a sneaky hex bolt actually in the motor attachment (see image below)
Once that bolt is out (you need to hold the motor attachment while unscrewing the bolt), you'll almost certainly find the offending blockage, this is a picture of mine...
Here's the full video for reference :