Some nice West Berlin boundary pictures, showing railway border
crossings, can be found at
http://www.signalverbindung.de/seite/zurueckbleiben.html . Look for
the caption 'Die Berliner Mauer aus der Bahnperspektive (1983 -
1988)'.
A.o., it's Steinstuecken again, and S-Bahn station Wollankstrasse (on
GDR territory, but exclusively in use by the W. Berlin travelling
public).
Peter S.