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Maybe RACV might be able to give you some advice if you were a member, worth trying i guess. Or find a good workshop that specializes in holden like Walkinshaw Performance.
they said there wasn't any sludging...in the slump
Anecdotally this a common problem post timing chain replacement,but hard to prove so I have learnt and still hearing. I never receive the expert report that they did I asked see this and asked for all of my service records including the one that should have happened when we bought the car....which didn't happen....so the car has gone 34000kms without a service ( because I was 7000kms over myself) I asked for 3 quotes ...1)what it would cost to replace with a new engine ...2) what it would cost for a recond engine and 3) a question that has never been asked what would you give me as a trade in and they fix it up to sell...I got 1 quote the recond $9200.....the verbal quote for replacing all the parts $8200...and with labour would by $13000. So it's sitting on the back of a tow truck...apparently because of the type of engine so i have been told ...there aren't any new ones in Australia...