Valve cover, oil cap, oil filter, oil drain plug, head gasket. Or it could be dirty transmission fluid which adds trans pan gasket, trans drain plug, trans cooler lines and/or their associated fittings. Bottom line is you need to get in there and look. There are just too many possibilities to guess at.
RepairPal Certified shops can diagnose and repair your 2003 Mercedes-Benz E320. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.