BC-
I was able to find a similar document for download via my school library. It is by some reliable folks at WVU. I turned one graph from their pdf file into an image, so I could post it here. It is a bit small, so let me know if you want me to upload a better version. The wear is not quite linear with soot, and I just didn't want to misinform anyone. The reference material is below.

Effect of diesel soot contaminated oil on engine wear
Sam George, Santhosh Balla, Mridul Gautam∗
Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown 26506, USA
Received 28 February 2006; received in revised form 22 September 2006; accepted 13 November 2006
Available online 6 December 2006
Abstract
Contamination of lubricating oil by diesel soot is one of the major causes of increased engine wear, especially with most engine manufacturers
opting for Exhaust Gas Recirculation (EGR) technology to curb oxides of nitrogen (NOx) emissions. The diesel soot interacts with engine oil
and ultimately leads to wear of engine parts. Factors which can change or modify the characteristics of the soot surface are expected to play an
important role in controlling the interactions with soot. Hence, it is important to study the interactions between soot and oil additives in order to
develop high performance diesel engine oils for engines equipped with EGR.
Astatistically designed experimentwas developed to study the effects of soot contaminated engine oil on wear. The variables that were considered
were the base stock (groups I and II), dispersant level, and zinc dithiophosphate (ZDP) level. The above three variables were formulated at two
levels: low (−1) and high (1), which resulted in 23 matrix (8 oil blends). In order to study the non-linear effect of soot, it was considered as a
variable and was tested at three levels: low (−1), medium (0), and high (1). This resulted in testing of 24 oil samples.
A three-body wear machine was used to simulate and estimate the extent of wear quantitatively. The extent of wear was measured as the actual
loss of material, in grams. A second set of experiments were performed on a milling machine (ball-on-flat disk setup). The wear scars formed
on the steel balls were examined using a scanning electron microscope (SEM) and were analyzed qualitatively to determine the effect of soot
contaminated oils on wear.
The results obtained were analyzed using the general linear model (GLM) procedure of the statistical analysis system (SAS) package to determine
the significance of variables on wear. The analysis indicated that wear increased nonlinearly as the amount of soot increased. Cumulative wear
was more for samples with soot contamination than without soot contamination. This showed a detrimental effect of soot on the oil blends wear
performance. The SAS analysis showed that the base stock and soot content were the most significant variables affecting wear. Dispersant and
ZDP levels were also found to be significant. The highest wear resulted from a sample that had 4% soot.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).