The oil use does sound overly excessive, id get down to your local workshop of choice, and ask for a leak down, and compresison test to be performed, this will show up potential problems pretty quickly..

Holden had issues with the HSV line up using the LS1 motors, a large number of them have had motor swaps because of excessive oil useage..

600ml in 1000km is a lot of oil, effectively, in 5-6 thousand km, eg half the normal service time, you will have used all the oil and run the motor dry..

thats a _lot_ of oil consumption going on there..

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