Gentlemen (and ladies), I realize that this issue has been hashed, hashed again, and rehashed over and over. Still, I hope someone can point me to a firm answer.
I have read the entire thread regarding oil change intervals. I have read SUNRG, DBW, and other's excellent posts regarding the fact that you should NOT change oil in a PD Jetta (2006), using 505.01 oil less than an interval of 10K (except for the first and second changes).
However, I have been told all my life that an engine lasts longer if you change the oil more frequently. So, since reading all this information, I have asked many, many diesel mechanics, oil salesmen, stealers, marine engine experts, and other owners when to change, and they all echo the shorter period---not necessarily because of the oil being bad, but because of possible contaminants from outside sources, or for other reasons (or, just because they too have been told that this is the best thing to do).
Could someone please tell me where I can find information that shows that the longer period is the best? Is it the oil analysis spreadsheet? Or somewhere else? An article perhaps?
I am NOT an oil expert, but just cannot understand how oil that has been "used" for 5K can be better for the next 5K than brand new oil and filter.
Thanks in advance,
John