My 06 VE Calais displayed the check engine light with 120k's on the clock and 3 months out of warranty, I had it checked and was told that the timing chain/s had stretched and would have to be replaced. I was quoted $2500.00 at the local dealer.
I calmly discussed this with the service manager and advised that if the engine had a timing belt I would accept that a replacement would be an acceptable outcome as belts do stretch and have a service life of around 100k, but as the Holden V6 has a chain, and it is a reasonable expectation that said chain, under normal driving conditions it would be reasonable to expect would last substantially longer than a timing belt (in actual fact I said for the life of the engine) then I requested that the chain/s be replaced under warranty. The server manager though about this and advised he would discuss with Holden and get back to me.
A couple of days later he rang and told me Holden had agreed and the chains were replaced under warranty.
I can only suggest you try this as it is reasonable to expect timing chains to last for the effective life of the engine under normal driving conditions, and letting it be known that you are aware of the under spec of the original chains used will help your case.
FYI, I had an SS exhaust, system, modified air intake on the car and a sticker on the back window from Gentech performance, so they could have taken the argument that I did not operate the car under "normal" conditions.
Call the dealers bluff as I believe that Holden know they do not stand on solid ground in refusing to repair under warranty.