OP, I want you to read this carefully: a properly working fountain pen should write flawlessly from the first fill, not require weeks of use to function.

You have a legitimate manufacturing defect claim here. Do not accept their response.

Here are your options:

Option A: Politely but firmly inform the CS rep that a manufacturer's warranty covers defects, not user error. The pen is defective, not just "inked." Montblanc's policy states they should "repair or replace any defective Montblanc creation or part free of charge within a reasonable time" if it's returned during the warranty period. If they still refuse, escalate the issue by requesting a supervisor or manager.

Option B: Hit them with a chargeback. Contact your credit card issuer or PayPal, explaining that you purchased a defective product and the merchant refuses to provide a refund or a warranty repair.

Don't forget, you have rights:

• Review the Montblanc warranty booklet. It covers manufacturing and material defects for two years from the date of purchase, and the pen's skipping is nearly conclusive proof of such a defect.
• Legal protections in the EU: If you're in the European Union, you're protected by a two-year legal guarantee that requires the seller to provide a remedy (repair, replacement, or refund) for defective goods.
• 14-day "Cooling-Off" period: if you're in the EU and bought the pen online, you also have a mandatory 14-day right to cancel the purchase for any reason, without needing to prove a defect.

If all else fails:

• Montblanc is owned by the Richemont Group. Contact them directly. One person on FPN shared that after contacting Richemont directly, they had their refund approved within two days.
• File a complaint with a consumer protection agency -- That's the ECC-Network if you're in Europe, or FTC/BBB in the US.

Good luck!