[SOLVED] Epson CX11NF laser smearing output with toner (toner recently replaced)

[itm]

I recently replaced the black toner cartridge on my Epson CX11NF multifunction. It's been fine for a few weeks, but is now smearing every printed page with a large streak of black/grey toner (a bit like a skidmark running from the top to the bottom of the page) - see image here:
https://drive.google.com/file/d/1zNMiu0T-OWfDOf2RRzVP2990hAc1LFOi/view?usp=sharing

I guess that this requires something to be cleaned or wiped - would anyone be able to offer any advice?

 

[Ralston18]

Original/genuine toner cartridge or generic/3rd party toner cartridge?

Even if "marked" as original/genuine the toner cartridge could be counterfeit. Source?

Does the following User Guide match your printer?

https://files.support.epson.com/pdf/cx11n_/cx11n_ba.pdf

[Do verify that I matched guide to printer.]

Sections/Chapters 7 (Page 79) & 8 (Page 99) should give you a good start on troubleshooting the streaking.

Toner is very messy as you probably already know so take precautions when opening things up.

 

[itm]

It was a 3rd party cartridge, from a seller on eBay (UK).
That guide does match my printer - many thanks for that - but those chapters didn't really give any clues re. my problem. I cleaned the relevant areas referred to from p91, and printed a number of pages containing a single character, but it hasn't resolved or reduced the problem.
I contacted Epson support, and they suggested that there may be a problem with the fuser, but couldn't be sure. It would be quite an expensive component to replace on a speculative basis!

 

[itm]

I also notice that the photoconductor is covered in black toner - see here:

https://photos.app.goo.gl/3gZDyLvayKC1hFQT9

If I I wipe it clean and print another page it's covered in black toner again. Is this normal, or could it be that toner has leaked from the black toner cartridge?