Mysterious oil leak

As I am not too familiar yet with these old cars, I was just wondering if anyone knew of a gasket or something in the lower part of the engine that tends to need changing with age due to oil leaks.

Reason why, is I have a leak and I can't find where it is coming from. I have changed the valve cover gasket and the washers on the oil drain plug and the oil filter and now I'm at a loss as to where this small drip is coming from. It doesn't appear to be the oil pan gasket.

Any help would be appreciated, I use Mobil 1 15W50 and it is expensive ! Not to mention I don't want anything to blow and then cost me a ton of money that could have been avoided.

Thanks in advance,

AARON ROCHARD

1976 230.4 W115