Please help me determine where the leak is coming from. I don't notice any oil on the driveway so it is a very slow leak. I hope this is not that rear engine seal everyone dreads!

 

Nothing from up top along the back of the head?

 

It's dark now so it is hard to see but I think you are on to something. Looking at the picture at the back of the engine is that the rocker cover gasket?

 

That's not uncommon but not enough to cause what you are seeing below. The rear of the head is basically the driver's side the way it sits in the car. If the can seals aren't leaking, it is probably the rear main. You should also make sure the breather box isn't clkgged, causing the leak. If there is positive pressure from the dipstick, replace the breather box and clean the ports on the block from the breather box and verify slight vacuum from the dipstick. Then clean off the oil and hope the seal isn't permanently leaking.