I am having the same problem troubleshooting right now. I have a recently purchased 1991 190e 2.6 with 88k miles. After driving it less than three hundred miles I discovered the coolant res was full of coolant and oil mixture. Again, clean coolant draining from the block, no overheating, engine runs very smooth, no white exhaust. I want to be sure there is no other possible cause for the cross contamination before goin ahead with the HG replacement.