They don't need spares because they never break.Parts scarcity? The TD42 was made until ~2010 IIRC (not for AU market) plus any time Nissan made them as spares; whereas the 1HD-T stopped back in the late 90s.
Toyota also had to cancel orders for 70s because even Toyota couldn't predict how wildly popular they'd be.
Had to laugh at how John Cadogan called the 300 an intelligence test.