Question about Samsung Portable SSD T3

It's a problem of that time. Many dark-coloured plastics "decompose" after about 10 years. You can try to remove the glue with rubbing alcohol. But it's quite a mess.

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Not sure this is your problem, but if you often hold the disk in your hands it could be the sweat on your hand. Some people, me included, have a somewhat corrosive sweat that over time it can damage some plastics. Alternatively some plastics simply don’t age well. Either way be careful with using chemicals, they may just make the problem worse. Perhaps you could just cover the black area with black tape.

Isopropanol probably works best. Otherwise cleaning alcohol, preferably high proof. Take care that nothing gets into the housing. Allow to dry well.