Kostecki will partner Bryce Fullwood in the #2 Mobil 1 Middy’s Racing entry, while veteran Warren Luff stays on for a seventh season with the squad, now alongside marquee recruit Chaz Mostert.
Luff had previously partnered Scott Pye, the duo finishing runner-up in the Supercheap Auto Bathurst 1000 in both 2017 and ’18.
The 43-year-old is a two-time winner of the PIRTEK Enduro Cup; a trophy Mostert also has on his resume, in 2017.
“It’s fantastic to be back with the team, alongside a new teammate in Chaz,” said Luff.
“There’s no doubt he is one of the top talents in the series, so I can’t wait to line up alongside him and see what we can achieve together.
“On the team front, we made some real ground towards the end of last year, so I’m confident that will continue in the early parts of 2020 and we can roll into the enduro season in a really strong position, fighting for trophies.”
Co-team principal Bruce Stewart sung Luff’s praises.
“Luffy is an outstanding talent and has done a faultless job in his time here, so we welcome him back with open arms,” he said.
Kostecki has raced in the main game in 2016 – as an injury replacement for Lee Holdsworth at Team 18 – and in ’18 as a wildcard entry, but this will be his maiden Enduro Cup.