I have a renault clio 52 reg, the engine coolant keeps goin down

I have a clio, had same problem too. its the head gasket. when this breaks or cracks it allows water into parts of the engine it should not, and therefore the water starts to mix with the oil forming this 'light brown gunge' the problem is that when driving with a damaged head gasket you will damage the head of the engine too which is why this is reoccuring. your best bet is to take apart the engine, clean it out, buy a new head gasket and then get the head of your engine skimmed. this could solve the problem depending on how damaged your head is.