Based on the description alone, the model cannot be unambiguously assigned, since the features mentioned apply to all Meisterstücks. With additional photos, collectors identify the pen as a Meisterstück 145, which has been produced for around 15 years and is therefore not considered old. The small additional spring in the piston converter is structurally present in order to overcome adhesion forces in new converters and to ensure continuous ink flow to the feed. Before first filling, a water rinse is possible but not strictly necessary.
Related pages on fountainpen.de:
• Montblanc Meisterstück 145 (Classique): fountainpen.de/c-montblanc-meisterstueck-145-en.htm