I discovered the source of my oil leak this morning: turned out to be the small oil pressure gauge tube, right where it connects to the top of the oil filter housing. It's a 14 mm nut that connects 'garden-hose-style' to the small, fairly hard, plastic tube that goes through the firewall to the oil pressure gauge.
With the engine running, there was a drop of oil coming out every second! That's a small puddle fairly quickly. I tried cutting off the end piece of the plastic hose to reconnect a fresh section to see whether that would cure it, but I could not manage to refit the plastic hose onto the metal fitting, even after having it sit in boiled water for a minute or so - that's how hard that plastic is (or has become).
I will order a complete new hose-with-fittings tomorrow and in the meantime I capped off the opening on the oil filter housing so I can continue driving the car in the meantime. No oil pressure reading of course (looks strange - but then again, I have never in my 9 years of ownership had an oil pressure problem).
