Who has to pay if spark plugs are defective before the maintenance interval?

Hello, my question as in the title, reason is that “allegedly” the ignition coils were leaking and water has come to the candles this has cleared itself with rust on the candles. Now was calculated for over 400€ for exchange of the 4 candles and 2 of the coils and troubleshooting. However, I am of the opinion the wear part which according to the maintenance interval are not yet on the warranty belong especially for the vehicle a long-term guarantee has been completed. Are I right there? Thanks already in advance for helpful answers