I too believe you should fix the leak and keep the car. I would use a engine degreaser and clean up any traces of oil. You could continue to monitor the leakage and fluid levels. Records for my 300CE indicate that the head gasket was leaking out oil as far back as 2003. I just had the top end rebuilt this year and it was still operating fine since the leak was external and did not affect the engine compression. If your car is in otherwise good health, I would go ahead and do the head gasket at a independent specialist. With that many miles you would be wise to check and replace the valve seals and guides if they have never been done. The M103 tends to have a weak spot with those two items.