Oil leak at bell housing—how to diagnose?
 

There's a film of fresh oil on the lowest part of my bell housing and it drips a bit. No more than several drops a day, but I'd like to at least know what's up.
Is there any way to tell whether it's the rear crank seal, torque converter, or trans front pump seal that's leaking without removing engine/trans from the car?

It looks dark, like motor oil, not red ATF, but I don't have records from the PO regarding trans fluid change, so I suppose it could be old sludgy ATF. The transmission shifts buttery-smooth and doesn't seem to have any power lag.

Probably trans front seal or support bushing... common.

Could be rear main or valve cover gasket. Also common.

Clean your Engine and the Bell Housing area.
Go for a drive and after the Engine cools down check the Valve Cover between the Fire Wall and the Back of the Engine.
Check the Oil Filter Base Gasket.

If it is only drippng at the Bell Houseing most likely the Rear Main Seal.