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There are a couple of possibilities for a leak in that area. One would be the rear main crankshaft oil seal. This is what seals the end of the crankshaft, and when it leaks it will come out in that area. To get to this seal you would remove the oil pan, the oil pump, and the rear main bearing cap and you would drive the upper seal half out of the engine block, and slide the lower half out of the lower main bearing cap. It's not a whole lot more work than just pulling the oil pan down.
Another possibility would be that the oil pan gasket wasn't in the correct position in the rear when the pan was installed. It's easy to knock the gasket out of position when putting the pan back up and it will leak. Also, any T joints need to have RTV sealer applied before putting the pan back up. The area where the rear main bearing cap mounts, at the left and right corners it should have had some RTV applied before the pan was put back up. Any area where three different planes of sealing surface come together always need RTV.
The crankshaft rotates in the engine block with main bearings. The main bearing caps are what holds the lower shells of the main bearings, these caps hold the crankshaft into the engine. The rear main bearing cap is the main bearing cap all the way at the rear of the engine. This is where the rear main seal is.
Disregard what I first mentioned about the rear main seal being a two piece design with an upper and lower seal. It's actually a one piece design, driven in over the end of the crankshaft from behind. This isn't removed by removing the oil pan or rear main cap like a two piece, this style of seal requires trans removal to replace since it's driven over the back of the crank.