Repeated content in narrow strip: Dirty fuser?

[NoHairInPrinter]

HP LaserJet Pro MFP 400 M425dn

The printer mostly prints fine but every time there is any content in a vertical stripe about 8 to 12 mm from the right edge of the page, it repeats several times across the page at even intervals, progressively fainter with each duplicate.

Demonstration of what the effect approximately looks like. Not to scale.

The distance between the marks is 56.9 mm (±0.3 mm measurement error), which would correspond to the circumference of a cylinder with diameter 18.1 ±0.1 mm, which is most likely the fuser. I suspect it is the result of contamination with sticky/oily residue. Dozens of cleaning pages have lowered the strength of this effect but not mitigated it entirely, so I bought some isopropyl alcohol to clean the printer. Are there any rolling parts I should be careful keep the IPA from? Given how difficult the fuser is to access, is it possible to disable the heater somehow and run a cleaning page lightly sprayed in IPA in the affected area? (The reason I don't want to do this when hot is fears of the IPA's thermal capacity causing uneven temperature and possible heat expansion problems.)
I am reasonably skilled at repair, do you think a cleaning or fuser film replacement is likely to help or does the entire fuser unit need replacing?

Also, users complain about the toner smell, especially when printing many-page documents. Is this normal? Do any other parts need cleaning/replacement?

I would like to use HP Device Toolbox for Windows which is referenced in the maintenance manual but it does not install when reinstalling the software using the official installer.