It’s really hard to say what part most likely have been water damaged, it may be almost everywhere in the device or just a connector.
Buying water damages devices is a gamble, you may get an easy one that needs a little bit of cleaning on one or a few places. Or it may be water damage almost everywhere and a lot of things that need a replacement.
What part that is most likely the place where it’s water damaged is difficult to say since it’s not really made to stop water from coming into the device, so it may have got to a lot of different places depending on how much water it was.
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Hope this helped, even though I didn’t really give you a clear answer. :D