Ok, I've dissasembled some of the Amiga 4000 (the Micronik board and the Retina). I can see the motherboard and what I see is not good. Take a look for yourselves:
I think it's safe to assume the WarpEngine and the Retina are in good shape (dust aside), but the motherboard has lots of damage. I have a contact cleaner spray handy, and I'll try to spray the affected mobo zones and clean it of all that green stuff and corrosion.