It was a fucking recall! Nissan did it to fix something they fucked up on they early model 300zx fuel injection system. They didn't want to call it a recall because that would look bad so it was called a service campaign. And they didn't really want to spend the money to do it to all Z31's so they said it was voluntary. Non the less, it was a god damn recall.
"Did you have the voluntary service campaign preformed on your Z?"