From what you just described it sounds like the oil is leaking from the valve cover gasket. I'm afraid I don't know what the torque specification is, but you should definitely snug up those bolts if they are loose. The valve cover nuts seem to have a tendancy to loosen up over time, at least they did on my 190E. If tightening the loose bolts you described doesn't stop the leak you probably just need a new valve cover gasket, which is an easy and inexpensive fix.