The Cook Strait ferry Kaitaki lost power in January due to an old engine part which ruptured.
RNZ can reveal just how many old parts were in its engines at the time.
Documents show three other rubber joints were as old or almost as old as the one that blew out. One had been made in 2007 and installed by KiwiRail's Interislander arm just two years ago in 2021.
Investigators have said these things start deteriorating straight away.
Reporter Phil Pennington spoke to Ingrid Hipkiss.
