Is it possible to have oil leak out of the rear main seal while the car is not running and just sitting? Seems to be coming from that area but was also wondering if it may be coming from the oil pan seal?

sure, the oil would trickel down and escape where ever its easiest to do so

Here is an upside down pic of the normal oil level. It is under the main seal but it could leak out the rear of the pan gasket (just under the main seal)when sitting. Unless you are running the oil level really high. The rear pan gasket under the main is quite often rubber with spikes/fins and have a habit of blowing out and leaking.