I’ll give Mainboard removal and reinstall a shot, sure. I see no harm in doing so.
As an aside, I have noticed something a bit strange about the lower chassis and I wanted to get y’all’s opinions on this. Upon looking closely at the edges, it seems like the enclosure curves slightly upwards at the corners. I took some pictures to illustrate:
If you notice, you can see the keys on the keyboard and some light shine through the bend in the center of the chassis. I used the edge of my portable monitor (which is perfectly flat) to make sure it was properly visible in the pictures.
The same thing happens at the opposite side of the chassis, as well as the front edge. I wonder if this could have to do with the decaying thermals.