Holden Astra Problems

I doubt very much that it is the head gasket; I reckon you would have seen the engine temperature rise if it was a leaking head gasket. You won't know until you actually pull it apart and check it, but I would suspect it's the water pump that's leaking.

Whatever you do, don't drive it, don't even start it. It's likely that you have done serious internal damage already and driving it, starting it even, would only damage it further. Have it towed to a mechanic and have the engine checked. I fear the damage extends well beyond the water pump.

The maintenance-free battery won't last any longer than any other battery, all it means is that you don't have to check the electrolyte level and top it up if its down. I wouldn't replace it until it's needed; if you are concerned have a mechanic test it to find out its condition.

The first thing you must do is to find the cause of the leak. Depending on what that cause proves to be you might then be in a position to approach Holden for help. Until you do that there's nothing Holden can do for you.

Holden tells us that the service interval for your engine is 10 years or 150,000 km, whichever comes up first. With 142,000 km up you are approaching the service point. Change the belt, and the water pump for safety, and that should be it.

It's odd that there's such a disparity between steady-state highway driving and round town use. If the performance has dropped off I would be checking things like the exhaust backpressure, which might show up a blocked or partially blocked catalytic converter; if the performance hasn't altered look at the oxygen sensors.

I wouldn’t necessarily relate the key failure to the crash repair; I think that’s probably a coincidence. If you still have the key you could take it to a locksmith who handles car keys and have them check it for you to see what has gone wrong with it.

Take it to a reputable mechanic and have them thoroughly check it, in particular they should check the crank angle sensor.

Almost certainly they were “recommended” by the dealer and not Holden, and furthermore they are what is known in the trade as “upselling”. They are not necessary.