When the pen was held completely under water during cleaning, on operating the piston mechanism water penetrates into the rear area (mechanism chamber). On renewed drawing-up this remaining water mixes with ink and then visibly emerges from the rear ring. Remedy is provided by repeated dry-wiping of the mechanism area after filling. If that does not help, a factory repair is necessary — Montblanc reliably remedies such defects. For disassembling the piston mechanism English-language guides exist (e.g. on fountainpennetwork.com); aids of soft wire (paper clips) are unsuitable; a cocktail fork with bent prongs or a dedicated mechanic's key are the better tools.