Hi there,
If it's on the driver's side it might just be the power steering pump or gear, or a leaky hose. My '79 450SL had a slight leak from the shaft seal on the pump, which allowed the oil to leak out from the shaft onto the pulley and then was thrown around pretty much the whole front of the engine. It was fairly easy and fast to change, a couple hours was all it took. So, the question is: are you checking your power steering fluid religiously, and is it going down??
A few drops from the valve covers seem to be very common on these engines, and indicate that the cover gaskets have hardened and need replaced.
Hope these ideas help!
PS - the pwr steering shaft seal was around $7.00.