They blog a lot about their repairs process in general. It's primarily mechanical damage to lenses they appear to normally deal in - the focusing rings, aperture mechanisms or realigning optical elements dislodged by drops and so on. An embedded CCD/CMOS sensor is probably a full logic board replacement I'd assume, as opposed to some kind of sensor only replacement, given it's almost always soldered on.

I know about 12 years ago I blew the firewire connection on my video camera (Canon xm2), and to fix it they would have to replace the full board.

So I feel like they don't make them repairable.

There are a lot of things that a professional repair shop focused on a particular type of equipment may be able to do that aren't practical for anyone else - including manufacturer repair facilities. Louis Rossman is a bit entertaining on this: https://m.youtube.com/watch?v=ocF_hrr83Oc

Yet with a heat gun its an easy fix.

It depends on their expertise