Holden Commodore Engine Problems

It sounds like it could be a problem with the brake master cylinder. Take it to a brake specialist who should be able to sort it out for you.

The warranty covers you if the car has a problem, Holden is obliged to honour it and give you a car that is trouble free. Beyond that there is a requirement for any manufacturer, of any goods, to produce a product that is of commercial quality. If the oil consumption of your car doesn't improve you could claim it's not fit for the purpose for which you bought it. But I wouldn't rely on our consumer laws to get you a result.

It's suffering from fuel surge, and I would be looking into the fuel tank, to the anti-surge fuel pot.

As it's not a consistent problem you would have to think there's an issue such as a connection or a sensor that's faulty. The factory system used by Holden is an Impco one, designed and developed by Impco for Holden. I would bypass the Holden dealer and go to an accredited Impco dealer and have them check it for you.
 

The oil consumption is way too high. The engine should be pulled down to find the cause, and I would suspect that it is related to the problem you previously had with the engine.

We checked around and found that there are reports of fuel quality issues resulting in injectors being blocked. The issue is thought to be predominately caused by contaminants in the gas leaching plasticizers from flexible rubber hoses installed on some LPG vehicles, which then migrates to the injectors. The recommendation we were given is to inspect the car's fuel delivery lines and if they are rubber check their extractability rating. If the rating is not near zero, then have them replaced with either copper lines or zero extractable flexible lines.

Clattering on start-up has been an on-going problem with the V8 Commodore and yours seems to be suffering from the same problem. Change the oil before you drive it anywhere, metal particles in the oil can lead to severe engine damage if not flushed out. Also talk to the dealer about the problem and demand it be fixed under the warranty.

It's not related to the fuel system as the Impco system starts on petrol every time, whether you've got the system switched to petrol or LPG. It's more likely to be an engine sensor, such as the crank angle sensor, which is playing up intermittently. Check the connections and the sensor itself. As for the warranty, you did the right thing in reporting while the warranty was in effect, so you could have a claim against Holden once the cause of the problem is  determined.

It does sound as though it is using too much oil. Sit down with the dealer and work out with them how they will tackle it, and press them for a solution. Also check the oil level weekly so you don't inadvertently run out of oil.

It's not possible to diagnose your problem with any certainty, the mechanic is obviously checking the things that do go wrong, but hasn't clicked on the right thing yet. I would have the crank angle sensor checked.