This is as good a place as any to ask, are there any good documentaries about how various stuff is made that isn't entirely fluff interviews & panning over assembly lines without any explanations about the engineering involved?

No humans speaking, just 90 minutes footage of the BMW i3 car production / assembly line. https://www.youtube.com/watch?v=29VHdcOvnK8

It's incredibly hard to find really good documentaries, they are basically all fluff pieces as you mentioned :/ I have however good experiences with old docu's on Youtube (propably made in the 80s/90s and digitized from video casette). These kind of docu's don't have as many bad interviews as modern ones and just have more content imo.

AgentJayZ on YouTube is amazing for understanding everything about jet engines/power turbines. Seriously great channel.

Thanks for that pointer - that is a seriously cool channel - I wasn't sure what to expect, but I'm really digging the videos discussing how to correctly assemble a jet engine.

How It's Made is decent. Not much actual engineering talk though.

In Germany we have "Die Sendung mit der Maus" and there the specific part "Sachgeschichten". It's primarily aimed at children, though. https://www.youtube.com/user/Sachgeschichten

All of it? It's an hour-long BBC documentary, I'd hope it has something useful.

Well, it shows how jet engines are made, and it's produced in the UK. Rolls-Royce are the UK's largest manufacturer of jet engines, so it makes sense it would be about their process rather than any other.