Remember, a 'Positive' Rating will not close this question, You can post a reply here whenever you want, even after rating my answer!. If you need additional information, don't hesitate to ask, I am happy to help as long as necessary to help solve your concern. So at this time, if you pull the inspection cover, you will only be able to see the general area of the leak, to be sure, you will need to pull the transmission.

To be sure where the oil is coming from, you would need to add oil leak detection dye to the oil and then run the vehicle, after driving for a bit, then you would use a flourescent light to find the source of the leak. Also the oil pan gasket can leak and result with oil dripping off the back of the engine also. If this O ring is leaking, the oil will drip off the left side of the back of the engine by the starter. There is a 'O' ring for the back of the camshaft, this o ring is positioned between the back of the block and the Transmission Mounting Adapter.

There are also a couple other scenarios that can result in oil dripping off the back of the engine. The only way to actually tell would be after removing the transmission and the Flex Plate, if the seal is back against the Flex Plate then the seal is backing out of the seal retainer, If the seal is in place on the retainer, and just leaking from the sealing surface, then the seal itself is leaking or the Crankshaft may be excessively grooved and leaking due to that.

5.9 cummins rear main seal towing