I was bored...
Writing instruments that have been damaged due to defect in any refill not recommended or manufactured by Faber-Castell, including ink stains and seized mechanisms;
Bolding is mine.
Montblanc offers an exclusive selection of different Montblanc ink colours. In order to best protect your Montblanc fountain pen from any damage, please only use the Montblanc ink.
This warranty also does not cover damage that is caused by the use of non PARKER® inks or refills.
Pelikan (sorry, didn't find web-link, so quoting a warranty slip which came with a m600 last year)
The warranty excludes normal wear and tear and becomes null and void if the writing instrument has been used inappropriately, manipulated by third parties, is lost, or will be used in combination of other than Pelikan accessories.
Namiki Pilot just recommends use of Namiki inks.
Sailor, Yard-o-led and Cross doesn't seem to have such clause.