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
You'll want page 11 in section "GW".
As a side note - make sure you take pictures before they touch your car as they managed to put a nice dent in my roof when they were fitting the new windscreen with a mallet....
Took me over 6 months to get them to pay for the repair!
Hope this helps you!