A rear main seal leak usually collects and drips from the Bell Housing of the Transmission.
The new kind of rear main seals they've been using in every engine designed since the 90's, last much longer and leak far less than the common rear main seal leak of years ago.
Like with any leak, clean the engine and compartment real well and keep going back looking for the leak where it starts. Leaks can be decieving because the fluid will always down, collect and drip from the lowest point. So where you see oil collected is NOT always the location of the leak, its just where the fluid is collecting as it runs down the engine.