Looks like things need to speed up.
Center pin cracked on at least 4 of the train sets, leading the fleet to be grounded.
The fleet as such is not going to be grounded, one set has been taken off the Grafton run which will be replaced by buses.
IIRC, there were two extra power cars that were purchased as spares/replacements for sets in need. The worst of this will be delays as they have to get the new pins supplied and fitted. Little doubt this issue shows the age of the fleet and especially the pressures on the power cars.
From my perspective, with this happening the government should bite the bullet and fast track the replacement fleet that will take over from the XPT eventually, once the pins are replaced and the units totally checked/overhauled they should keep going for some years fairly well free of issues.
Passengers don't really feel the track affects on the carriages except when walking through the cars when at speed. Get up front in the cab and its a totally different experience with the ride you get/got and that's likely different today to when I was driving them owing to the better overall track conditions of the day.