That's the question. The ULSD requirement came with a lubricity standard. Sulfur's impact on lubricity is no secret.

What, exactly, would cause a leak with ULSD? Folks are quick to blame sudden leaks on the nearest possible cause (fuel change). I am not saying's it's not ULSD, but I cant think it is until I understand a concrete theory.

If had a fuel leak today, but it turned out to be a loose fuel hose clamp. I was quick to think ULSD for a second there.