To me its a flaw if its leaking so bad you have to start adding a lot of oil in between oil changes, say 2 quarts or more. I've been around a lot of engines, including a Cummins, and I've seen a lot of gaskets, seals and what not leak. I had a 70 Challenger with a 383 rear main seal that was a rope seal, probably the factory original, that leaked. Didn't mean the engine was junk. I've NEVER heard of a design flaw on the Cummins rear manin seal until this thread. Must be a problem on the newer 6.7 engines because I never heard of it on the 5.9's.