What color is the smoke? What kind of smoke is it?

Here is all the videos I have.

These videos are what I have so far

https://youtu.be/qvXef18mWnY

This was when I drove to the alignment shop and it started, there's not much too see really but it appears to be around the same place

https://youtu.be/DYyw_6hfOkY

I have other videos on another phone but I remember holding the RPM a tad to maybe 1500rpm and it made no difference to the smoke, not that I could tell anyway.

Okay, so I was having a mooch and I found that Injector 6 looked a bit wet. I then couldn't help but notice there's a.. Half circle opening on the valve cover design and I wondered if diesel could fill that much that it could eventually spill down to the back left.

Anyway, cleaned it like this:

https://youtu.be/S1VAr70os-E

I'm cleaning the back to see if the path of the diesel fuel does actually overfill onto it.

So with toilet roll shoved down by injectors 4, 5 and 6 and decided to idle and maybe see if I could spot anything, but literally 30 seconds after starting my toilet roll was drenched, it just looks like raw diesel..

https://youtu.be/d6g4F78rsqo

That's definitely raw diesel.

The smoke video did not look like an exhaust leak to me. Didn't sound like one either. The exhaust manifold doesn't look like it's leaking.

That's good to know, I was frustrated to see that the valve cover looks leak free and have to pull everything apart again. I suppose raw diesel leaves either hard-line or return line. While I will probably spot this tomorrow, would it make more sense for this to be return line given that I have no starting issues, MPG according to trip is about right and return line wouldn't give any faults, it would just be noticed on the fuel tank needle?

Do you also think that under the right conditions (enough diesel pooled, going up hills/over bumps) that the diesel would go over that half circle and down the back left by exhaust to explain the randomly occurring smoking.

I don't think you'd notice it on the fuel tank needle. That would be a massive leak. Without long term mpg calculations or knowing what the truck is capable of, there's no way to know if it's substantial enough to be an issue or if it affects economy. Who knows when it spills over where it drains to or where the wind blows it.

It's the return line:

https://youtu.be/tVleFfIaT4w

Why though I'm not sure, I've replaced the tiny nipple O-ring and from the video it looks like it's gushing from the top down. I couldnt see any cracks when I removed the white collar. BMW want £135 for the return line, I'm wondering if its not too much faffing if I can out my E90 one on and see if it sorts the problem.