Hi and welcome.
The page (in the French language) you're referring to, has 2 warnings:
To not mount it on metallic surfaces as that will distort the transmissions.
And to keep it dry, moisture will do damage to the battery and/or the electronics.
There's no way to tell whether this unit can be salvaged without seeing in what state it is.
Water will do severe damage real fast with electronics which are powered.
You may be able to fix it by removing the oxidised conductors, but you'll never be sure the fix will be permanent.
There may very well be places with damage you can't reach to clean, and re-powering it could restart the electrochemical reaction leading to further damage.
Electronics that got wet while not powered, may be rescued by putting it in a drying oven for a day or so.
Such oven would not be too hot, less than 80 degrees centigrade should be OK to the electronics, but plastics may have trouble with that.