I think you need to go on an inspection mission! Follow this IFIXIT guide: [guide|6667] and look at the edge where the water likely splashed in through the bottom vent holes. Take some good detailed images of the area. If you don't see anything visible on the top side we'll likely y need to put the logic board out to see the bottom side.
[guide|21499]
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=== Update (04/22/2018) ===
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OK, I don't see anything either, which is good!
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I'm wondering if your PRAM battery just needs replacement. Get a fresh battery and put your system back together did that fix it?
I think you need to go on an inspection mission! Follow this IFIXIT guide: [guide|6667] and look at the edge where the water likely splashed in through the bottom vent holes. Take some good detailed images of the area. If you don't see anything visible on the top side we'll likely y need to put the logic board out to see the bottom side.
[guide|21499]