The first response of most mechanics on this would be that you have a head gasket leak in the engine. Coolant in the oil and/or oil in the coolant are classic symptoms of this. It happens because the faulty head gasket allows the two fluids to mix but, depending on exactly where the gasket fails, you don’t necessary get both symptoms. A workshop can pressure test the engine’s cooling system and perform what’s called a TK test to show up any contaminants in the coolant that have found their way there via a blown head gasket.

But before you go tearing into the engine, check the service records to find out how old the coolant is. Coolant will discolour over time and kilometres and what you’re seeing as a `milky colour’ might simply be old coolant that has gone cloudy and needs changing.

 The odometer reading is on the high side of average, which would affect the value. It was also depend on the condition of the car. As a private sale you would probably get $3000-$3500, as a trade-in $1500-$1800.

You appear to have been given the run-around. Take the car back to the dealer and ask for a meeting with the service manager. Ask him for an explanation of what has happened and why, and then try to get a commitment to fix it, at their expense. You could also complain to the Motor Trade Association of WA about the work that has been done, they might be able to help you. You could also seek the advice of the WA Consumer Affairs Department, and as a last resort seek legal advice.