Take a look at the Moss catalog diagrams again. There is the oil pressure gauge sensor line that comes off the engine just below the oil pump outlet banjo bolt/oil fitting. This is a pressurized hose and has been known to be an oil leakage point. It fits with your general location description. With the Moss reference, you might be able to tell whether the hose has developed a leak or not. If the car is equiped with an oil cooler, then the oil outlet from the oil pump is in the same general location, but a little higher and larger. There is the clutch slave line too, but it is the lowest and kind of under the starter.
A cleaning of the engine and engine compartment can be helpful in finding engine leaks. Do this with some "Gunk" engine cleaner and a garden hose. Need to do this somewhere where the runoff won't hurt anything. Gravel drive, old driveway, yard, street or the like. Do this with the engine warm. Not real hot, but good and warm. Mark where the plug wire go using masking tape and a pen. Write plug cylinder # on the tape. Cover the distributor and wires with an old bread bag or grocery store type plastic bag. Cover carb inlets the same way. Spray the cleaner on the engine, let sit for about 15-20 minutes and then hose off. If you let your garden hose sit in the sun, then the water will heat up and act like a hot pressure washer. The longer the hose, the more the heated water.
Good luck, Mike