Built up water corrosion on a board can cause further damage if it is not cleaned and treated correctly. This laptop motherboard had water spilt on it. I was able to clean up all of the corrosion by using 99% IPA and a toothbursh.
The customer for this repair booked in as they had spilt milk inside the PC from the top air vents. This has dripped down mainly onto the GPU and dried. Surprisingly, no parts needed replacing for this, with a thorough cleaning of all parts stained in milk and a full clean of all dust, the machine was back up and running and completely dust free!