Nissan specify, in their workshop manual, that the rubber trim, rubber dam and plastic fastener should all be replaced whenever the windscreen is.   I had my windscreen replaced last year and showed them the workshop manual and insisted they replace the parts. They agreed to pay for and change the parts and I asked to see the new parts before fitting to confirm.   You can find the workshop manual here: http://www.allcarmanuals.com/factory-service-manual-61-Nissan-350Z-Fairlady-Z-Z33.html Y