I experienced a head gasket leakage a year ago on my 1995 S320L and it was quite hard to find the leakage source until I took off the underhood which carried the leak oil. It is resonable that you could not see any oil underneath. Mine S320L had it on 20,000 miles and was told by the Mercedes mechanics that it is a common fault of that engines and a new modified gasket had launched to make sure that the leakage would not happen so early. So, you should have a peace of mind for quite a long time after replacement. that leakage is not dangerous at all as long as there is adequate oil in your engine but just a little annoying.
Hope this helps!!
[Edited by Davis Lo on 04-26-2001 at 04:09 PM]