As Jimy Neutron suggests, look at the spill pipes. I thought I had an oil leak until I checked under the bonnet. Noticed oily black stuff coming from the bottom of the front injector, but on further looking noticed it was actually diesel coming from the spill pipe which had come off a little. Putting it back helped, but then my wife said she could hear a high pitched whistle (I'm actually partly deaf) so I pulled the rubber pipe off and then pulled back the woven cover to discover it had perished in 3 or 4 places. The diesel soaks old dirt off and looks like oil , well diesel effectively is oil, drips down and looks like it's leaking from somewhere else. £2 for a new length of pipe from local dealer, cut to length, put on and voila clean engine!