Used UV fluid to find an oil leak. Have only poured in the fresh oil, I have NOT started the car. There is a line along the transmission/engine mating point on the drivers side only.

I have a small puddle underneath the car as well. It has just sat for a day. There is a very small amount of oil sitting on the very back corner of the drivers side valve cover as well that I thought the oil was coming from but it looks like the oil coming from between the trans and engine just stops at the highest point between the 2. Could it be the head gasket on the drivers side? The rear main? or maybe just the valve covers dripping onto that spot? Anyone else had this type of leak and found out what it was?