A comparison between using tracers to detect wear and UOAs, and another article on Fe in sludge, although from using biodiesel.
A UOA not detecting wear / failure would be a 'false negative', while I'm assuming that the higher Fe in M1 is a 'false positive', so to be fair it's a different issue. M1 is often observed to 'keep engines clean', so perhaps it's also good at keeping stuff suspended in oil instead of allowing it to develop as varnish or sludge.
http://www.springerlink.com/content/pp66225734334nk5/
Quantitative Filter Debris Analysis (QFDA) as a means of monitoring wear in oil-lubricated systems
Received: 21 December 1993
Abstract In this study, the trace analytical technique of instrumental neutron activation analysis (INAA), using the SLOWPOKE-2 Facility at RMC, was used to develop an application termed Quantitative Filter Debris Analysis (QFDA). The preliminary step, which consisted of the quantitative analysis of filter debris samples from CH-124 Sea King helicopter main gear boxes (MGB) for 19 elements associated with engine wear, confirmed that distinct ranges of normal and abnormal wear rates exist in the CH-124 MGB and, more importantly, validated the INAA procedures. The second step, which consisted of the analysis of both oil and filter debris samples from the CF-188 Hornet aircraft engine by the INAA technique and an Atomic Emission (AE) method, confirmed that little useful wear information can be found in the oil of a finely-filtered engine system and demonstrated the potential of QFDA as a means of monitoring wear by analyzing the oil filter debris. What appears to be normal wear rate ranges were identified for the CF-188 Hornet aircraft engine. The potential of monitoring the wear health of oil-lubricated systems using QFDA was confirmed by this investigation.
http://www.senternovem.nl/mmfiles/OperteardownB20eng_tcm24-187057.pdf
Sludge Analysis
Analyses were performed to identify the source of the sludge. These included elemental analysis by inductively coupled plasma atomic emission spectroscopy (ICP, via ASTM D4951), infrared spectroscopy (FTIR-ATR), and isotopic analysis by accelerator mass spectrometry (AMS).
Results of the elemental analyses allow comparison of elements present in the sludge with those present in the engine lubricant (Table 4). This analysis was conducted on the two sludge samples from the B20 engines and the engine oil samples from all four engines. Considering that the B20 engines operated on B20 for 4 years, ending in 2003, the engine oil samples would not be expected to exhibit effects from B20 but to be indicative of engine wear issues with other causes.
The engine oil typically contains calcium and/or magnesium from the detergent and zinc and phosphorus from the ZDDP anti-wear additive; all these metals were evident in the analysis. The sludge appeared to be enriched in calcium and zinc relative to the oils, with zinc and phosphorus present in roughly the correct proportions for ZDDP. Iron in the used oil samples was low, so wear problems were not evident. Iron was concentrated in the valve deck sludge, but these levels were also low and probably not indicative of a wear problem.
