Kostecki was hit from behind by David Reynolds at the hairpin during the second Saturday race, leaving the championship contender to limp home last.
While the team worked deep into Saturday night to repair the car, Kostecki suspected lingering damage from the incident was behind his lacklustre Sunday performance.
Kostecki qualified fifth but could manage no better than 12th in the race, complaining of ill-handling.
DJR co-owner Ryan Story said the team will fit a new rear chassis clip to Kostecki’s Mustang ahead of the Darwin Triple Crown.
“The rear clip, we suspect when we get it crack tested, it’ll have some hairline fractures in a couple of tubes,” Story said on PG & The Doc.
“When that car was back on track the next day, pretty early into that quali stint, Brodie said ‘there’s something not quite right here’.
“We’ll put a new rear clip on the car for Darwin and that rear clip will get sent away to get crack tested and we’ll understand the extent of that damage.”
Kostecki’s Sunday race was also compromised by a refuelling issue in his first pit stop that necessitated an economy run in the second stint.
Story said his team has identified the cause of that problem, which has also tripped up others since the introduction of the fuel churns at the start of last year.
“Other teams have had similar issues with vapour lock with those churns, as recently as the New Zealand events,” he said.
“You have to be really careful with how you hold them and how you position them and have to ensure you get a clean fit with the dry locks when you mount the churn to the car.
“It doesn’t take much to be out, but holding it in the right position is critical.”
Kostecki sits third in the championship after five rounds, 173 points adrift of leader Broc Feeney.
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