How does your car run? Good, fair, poor? You mentioned that the inside of the tailpipe is black. That's a good indication that something is causing your fuel mixture to be on the rich side. How long has it been since you did a complete tune-up on the engine and cleaned the fuel injectors? An engine that is in poor tune can cause exhaust odor to increase since some amount of raw fuel can be mixed with burn't fuel, especially if the injectors aren't operating up to par.
How about the gasoline in Australia. Have any recent changes been made to the gasoline formulation in Aus. such as the addition of Methanol??
What year is your MKII? Is your check engine light coming On? I also have a suspicion that you may have a bad 02 (oxygen) sensor that may be causing your air/fuel mixture to be running a bit rich most of, if not all of the time.