Might be what you mention.

Have a close look at the selector shaft seal (LHS), the dipstick tube seal and the oil cooler lines as well. The oil level (running or otherwise) as you say is higher than the pan gasket, so if it is even slightly sus it will leak...

I'd be getting in there tomorrow with a can of carby cleaner and rags around the area you feel it is leaking and making it very clean to help with diagnosis.

Failing that have a good look to see if the vac modulator thread isn't leaking or if it isn't dropping out of the oil pump gasket/o-ring seal or the converter seal and running down onto the top edge of the pan area and making its way around the pan gasket? I've just replaced both the oil pump seal, gasket and my converter seal for something similar - much easier while I have the engine out.

You're on the right track!

Dave