Hi and welcome to the community forum 
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As to your specific problem, personally I wouldn’t go as far as bathing the modules, certainly not the display unit or the battery, but certainly use cotton buds soaked in isopropanol or surgical-grade alcohol (90°) for thorough cleaning. Larger pieces of cloth too, as long as it won’t leave anything behind (lint, other fibres …)
You mention a FP5 but then FP3. For present purposes it’s not that important but could you confirm which model this is about?
As to opening the modules, that depends rather on how much water got in and for how long. The FP5 resists water a little better than the FP3, but neither is designed to withstand total immersion. You certainly need to be sure no moisture is left inside the modules. Of course dry components thoroughly before reassembling the modules.
Once you’ve cleaned as well as you can, the important thing is to leave ample time for drying, preferably in a gentle flow of dry air. Use a clean cake rack or similar (minimum contact, maximum exposure to air). I’d say 12 hours in this case. Usually one would allow less, if you’ve just been cleaning contacts but here you’ll need more time I would think, to be on the safe side.