The leak you mentioned is very typical on the OM603.XXx motor. Is it somewhere around the 1st and 2nd intake vales?
It is not a big deal but if you want a bone dry engine, replace the gasket. Once you have the thing off, you might consider
1. clean the intake manifold
2. replace the glow plugs (only $8 a piece)
3. replace the shut-off value (also not expensive).