If its turning milky and oily then your engine head gasket is leaking engine oil in water chamber which in turn changing color and properties of coolant.
It is very serious and abnormal, show to mechanic for checking if your engine head gasket need change.
Sharjah industrial area behind BM road and another one behind the Al falah plaza have some Audi;s scrap yard. If its older Quattro you might get lucky, if new then chances are very less.