Now I have seen this box from the front I would like to add this:
The 'discolouration' on the front seems to be around areas where input sockets are located, is there any discolouration around any of the knobs, A/C socket etc? The box I have with this discolouration (quite small areas compared to the BB pictured) has the problem limited to the top around the control knobs and, when it first arrived, there was some kind of semi-congealed 'garage smelling' (oil/solvent/grease/diesel/etc.?) tacky gloop just under the control knobs in the same areas. I'm wondering if whatever caused this problem was also on the fingers of a former user of the BB?
The other point to consider would be if the discolouration agent has penetrated inside the box and caused any problems there. The first pic looks as if the box has been sat in a puddle at a backward lean so I'd like to see more pics, including inside the box, before I made any commitment to purchase. We can see how the outside painted plastic has been affected but what about other components?