I left the PIs at room temperature for a long time and then make them take a bath in isopropylalcohol. The RPI3 is OK again, the RPI2 not. It will take some time till I will risk a RPI3 outside.
Any idea what I could do with the RPI2 before scraping it? The only way I know to repair electronics is a bath in isopropylalcohol (surprisingly good results, about 10%). I heard about cleaning it with baking soda and about putting it for some time into a hot oven. And then I read the best idea is to ask the manufacturer.