Oil leaks on top of the engine flow to the back of the valley through a hole into the bellhousing / clutch area. It then drains past the rear main seal.

I have personally seen the orings leaking on 3 different 7.3 engines. The result was severe leaks from the bellhousing of the transmission, as if the RMS was bad. Some orings (at about $1.37ea for 6) is cheaper than just one RMS. Labor is cheaper, too.

These engines will shut down before the oil gets low enough to damage them.

As stated before, there are other, more likely possibilities for an oil leak than the Rear Main Seal. Check everything else first.