When you had it open, did there appear to be any liquid on the actual board? This sounds like something messing with thermal sensor data if the machine is throttling like that.
At the very minimum I would want to take the board out and check and see if there was any signs of liquid contact, corrosion or otherwise. I would limit or eliminate usage until you can do this, especially if you’re not sure if the board is all the way dry. It sounds like damage may have been minimal, but I would want to know for sure. It’s possible just cleaning up the board might be all it needs.