Spotted PBGY 0004 on Aurizon's 7BM7 this afternoon with a freshly refurbished roof.
It looks like a thick waterproof material has been applied thickly over the existing roof, probably to prevent rusting and potential water leaks, since there is a flat section longitudinally on the roof.
It isn't easy to pick from ground height, but stands out from an overbridge. I understand that a few others have received the same treatment during July.
It would be an easy alteration for ultra-modern modellers who run an SCT box train or an Aurizon east coast superfreighter.