You got it! If you need help in putting the ScooterHacking firmware you can ask me, I've done it on mine. Field weakening is incredible.
Another useful website I found is Joey's wiki, and finally Ninebot Max playlist on yt is not bad at all, the repair videos are short but well done (I yt-dlp the whole playlist :D)
Btw I saved your post because mine wobbles a bit, so I might have to look into the same problem in the future (and I already tightened the locking mechanism)
Hello, I'm seeing a T540P W540 W541 "Power Jack cable" available for less than 5 bucks (aliexpress, ebay, etc). The cable has the charging port and a connector that goes on the mobo so should be a pretty easy fix, no soldering.
Do you have the HMM (hardware maintenance manual) downloaded to double check?
Btw you don't need the whole "lenovo square tip" charger if you have a 20V capable USB C PD charger (65W or more), you can get a 3 bucks adapter, I use it all the time it works perfectly.