oil in water on M102 2.3 motor '89

Help ,I am getting oil in the water but not water in the oil.The car is also running like a dream a most upsetting state of affairs.The car has covered 134,000 miles with full MB service record and it uses only a litre of oil between 6,000 mile changes so I assume the engine is in good health.The dealer has had a look and says it is the head gasket starting to go and to leave it until it develops into an issue.Cost of doing gasket £550 ($800).I phoned an independent who said that it is fairly common for corrosion to eat away the head between oil/water channels at the back of no4 cylinder and at that mileage the head could probabley do with new valve guides and that it would be a good thing to replace the timming chain and tensioner at the same time!!!!He was very fair because he told me this was the worst case and it might not be so bad once the head was off.Cost £763 ($1100) but reducing if things did not need doing.He also said to get it done sooner rather than latter.The only sign of the problem is a slight oily feel around the top the expansion bottle and occasional light mayonnase deposit on the expansion cap,no water in oil,no loss of power or drop in gas mileage.
I feel like pushing the bloody thing off a cliff so I would greatly value your opinions about the best course of action to take.What do you think about using radiator additives in the water?
many thanks in advance
HAMISH