Hi Stanley89,
Wow, no response since your post here of a month ago.
Sorry about that.
Please read our Art Benstein's notes on the Volvo 240 wiper system foibles and resolutions (copy and paste URL into a new web browser tab or window - too lazy to make a link and target _BLANK - a new window for you):
Notes on 240 Volvo Windscreen Wipers
https://cleanflametrap.com/wiper.html
Notes on 240 Volvo Windscreen Wiper Shaft Repair
http://cleanflametrap.com/wiper93.html
I'll the issue is a lack of lubrication between the wiper rotating spindle and the bushing it passes through. The wiper arm secures to the spindle at the threaded end with a nut as you know.
You will want to use the search feature here and find other posts and threads on 240 wipers to help you.
The 240 OEM wiper motor is NLA from the OEM.
There is an aftermarket made by RONAK, sometimes sold as MTC, and I've read folks may have issues with the new motors. Probably because of wiper spindle and busing shaft lubrication.
A link to the FCP Euro sale page for the 240 RONAK - MTC wiper motor:
https://www.fcpeuro.com/products/volvo-windshield-wiper-motor-240-260-242-244-245-262-264-271863-1

Please see Art's you tube video of the honking wipers indicating a lack of lubrication. The honk-honk makes me LOL each time. Riotous! And then you feel sorry for the poor wiper system straining to make a go of it! I'll guess Art was gather and outlining the notes for his two aforementioned 240 wiper cleanflametrap.com articles.
https://youtu.be/i98fHSExTf4
I've yet to get under the dash specifically for this issue - to lube the spindle and shaft with grease. May not need to clean it.
Yet there do exist factory installed flexible white plastic caps to seal out water and weather intrusion that you see with the wiper arm removed. Sometimes these show fractures with age and exposure. You can get these as replacements. I cannot find this somewhat recent article using the search feature.
I found these caps mostly failed on my three rotting away 240s. So, my solution is to twice yearly in warm weather drip some Mobile 1 15W50 synthetic on the seam between the rotating spindle and the metal (bronze? sintered?) bushing.
Two not so great images:
Wiper arm removed. See the seal and the cap before removal

See the circlip? I rotated the circlip so the open end of it is up. And drip the 15W50 or whatever oil lube you use from small bottle into the seam between the rotating spindle and the bushing.

I remove both wiper arms. Drip a few drops in as fast as the oil seaps into the seam between the rotating spindle and the bushing. Turn on the wiper and continue to drip oil in.
These wipers on the 1991 240 shown were never seized.
If the wiper are seized or are seizing, may cause the motor to draw more current than the #Two 16 AMP fuse allows.
Also, the RONAK - MTC brand wiper motor has issues that some report such as poor build quality and internal shorts.
The other cause of fault with 240 wipers is that the factory wiper motor failed for a few reasons. See Art's articles.

Questions?
Hope that helps.
MacDuffed.
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Jonathan Harshman Winters III: The Mightiest, Greatest, & Most Powerful North American Comedian & Comedic Actor in Perpetuity
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