This can also be the case if your rear main seal has been compromised. At the same time, though, car maintenance can be a tricky matter, and it's rarely plain and simple like this.

If oil isn’t dripping from beneath your Jeep TJ’s inline-six, it’s because it’s either brand new or the rear main seal has been replaced within the last 40,000 miles. That’s just a fact ...

Before that, the rear main oil seal had been a two-piece design. The problem with the two-piece seal is that it can sometimes allow oil to seep out.