Its great to go down a rabbit hole online sometimes isn't it? 

Have you tested continuity in the bin?

I just asked our engineer and showed him your video and photos.

He feels the top bearing is shot and the commutator *might* be OK. That would account for some of the noise there, and certainly the sparking. However, without replacing the top bearing and bench testing it, there is no other way to know if the commutator is too far gone or not. Only when the bearing is fixed and the armature runs true will you know if the sparking subsides.

This has happened 2x now with Quаltex motors. 

We very seldom source from them anymore. Their motors aren't what they were. If you have bought from eBay or Amazon from them, I'd expect AI-type replies as they do a lot of volume and it's probably not cost-effective to pay people to answer the questions.

It's really hard to find good YDK-type Dyson motors at the moment. They have suffered a race to the bottom on pricing by all the big suppliers, and that means quality has taken a hit. As the machines are getting older, and people don't want to pay a lot for a motor, nobody will invest in better ones.

If we do a refurbished Dyson cylinder, I'd rather put a good used genuine one in than an aftermarket new one.

I'd be interested as well, like you say they're not hard to do but some prior knowledge of what usually still works and what might not would be really useful. I was pleasantly surprised the first time I opened a Sebo up - they do seem made to be repaired [and to go back together again - so much is effectively throw-away now].