The O-ring in question was only seven years old.

Even though ULSD does meet the specs, these motors (and their rubber components) were not designed in the time when diesel had a maximum of 15ppm sulfur and the minimum amount of additives needed to meet ASTM specs.

Maybe I wasn't clear, the lubricity of ULSD has nothing to do with leaking seals. Lubricity has to do with the potential of increased wear of the metal components (i.e., injection pump), and I have not seen any evidence that this is a valid concern for these engines.

The tendency of seals to leak with ULSD is a completely separate issue (nothing to do with lubricity). I agree that ULSD may adversely effect seals that are already degraded, and there has been a ton of information published on this. I replaced my IP a few months after ULSD came out due to an internal fuel leak, and ULSD may well have been the "last straw." However, I'm not going to whine about having to replace an IP with over 300K miles, and I'm certainly not going to start burning cooking oil/ SVO/ WVO/ ATF/ 2-stroke oil/ whatever just because I'm afraid that another 25 year old seal will leak someday. I'm sure something else will eventually leak, and I'll fix it when it does....BFD