Extreme water damage guidance

I just bought a DJI mini 3 pro that turns out to have severe water damage (it's a little complicated, but I'm not too disappointed). Shockingly, it mostly works (no errors, only the rear right motor has a little more resistance than the rest so it can't quite fly); the previous owner didn't even know it was water damaged. It's been at least a week since it got wet, likely much longer. I'm going to follow this tutorial to clean off the motherboard, replace the ESC entirely, and probably follow the same steps for the camera module (is this safe?). However I have a couple questions:

1. What is that white stuff? It seems to have been used to glue some of the connectors, but whoever did this obviously didn't actually fix the water damage.
2. Should I do anything extra/differently because it's been corroding so long?
3. Can I do anything for the motors (flight and gimbal)?
4. Are there any listings for the thermal paste on amazon that could arrive quicker with prime? I couldn't find any.