This is the OEM Fuel Dampener. If you have a black Dampener, it's original and many years old. It's a good idea to replace these when doing maintenance on your Z32.
The Fuel Dampener reduces fuel pressure pulsation in the fuel feed line between the fuel filter and injectors. Once these fail or get clogged; the idle starts to become erratic, and will cause poor performance.
Please be aware that Nissan / Nismo / Infiniti pricing is subject to change.