My 98 Audi has oil in the coolant but the oil is clean and it does not overheat. I replaced the front cam seals and the oil pump drive bearing and water pump, but found no way for the contamination. No loss of compression.
You can still get oil into the coolant through a head gasket leak, even if you don't have any other symptoms. You symptom of oil into the water is very classic of a head gasket leak. Oil pressure is almost always higher than the water pressure. If it's a small leak, oil can be pushed into coolant galleys, but not the opposite. If you have flushed your coolant system and the oil keeps returning, this is where I'd say your problem lies.
The Audis have an engine oil cooler cooled by the engine coolant. Look on the front of the engine just above the sump for two water hoses going to a three inch square finned aluminium box. This is the oil cooler. They can oxidise and corrode after time. They then allow oil to seep out under pressure into the coolant.