Oil leak mystery above subframe

Car had been sitting for the last 10 years have done some work over the last 6 months. Finally did an oil change to get all that old smelly oil out and have found after changing it I now have a leak from an unknown area not anything around the head gasket but it’s dripping onto the subframe. The oil smelt like old gas and had 10 litres plus when drained. Lots of sludge build up on subframe and drips the clean oil just off centre to the right a little.