It's on the NEC German (English) website, left column, bottom.
NEC Firmware Page
I haven't tried it yet, I just found it.
Direct Link for Download:
ND-2510A Firmwareupdate 2.16 (376.59 Kb)
Update: I just flashed it. I have this drive in an external USB 2.0 enclosure, and when I tried it there I received a "Flashing Error" and I thought, "Oh great, I just toasted it." So I hooked it up internally, was relieved to see the drive was still recognized (at 2.15), so I tried it again and this time it went through, and is now reported at 2.16. There's nothing I can find on their website to say what was fixed, though.
NEC Firmware Page
I haven't tried it yet, I just found it.
Direct Link for Download:
ND-2510A Firmwareupdate 2.16 (376.59 Kb)
Update: I just flashed it. I have this drive in an external USB 2.0 enclosure, and when I tried it there I received a "Flashing Error" and I thought, "Oh great, I just toasted it." So I hooked it up internally, was relieved to see the drive was still recognized (at 2.15), so I tried it again and this time it went through, and is now reported at 2.16. There's nothing I can find on their website to say what was fixed, though.