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dweller and unkl300d,
I am sure the little spring loaded check valve in the return flow tube is important to proper functioning of the filter. For example, if the valve fails to open the whole top two thirds of the filter becomes inert, as no oil can flow through it. All the oil has to pass through the bottom, less restrictive part, which means the oil does not get cleaned as intended. That will eventually lead to accelerated wear of the engine's bearings and other critical parts.
However, if the check valve is plugged there is no mechanism to generate a force to collapse the upper can. Remember, it is perforated to allow oil to pass into the filtering media, so if there is no flow, the pressure on both sides of the can will be equal and there is no reason for it to deform. Also, the restriction of the orifice in the side of the return flow tube would normally make the pressure drop across the filter element very low, exposing the grommet seal to nearly the maximum oil pressure most of the time. So it is unlikely the plugged line will cause the grommet to fail either, but I guess it is possible. This would still not explain the Mann filter being immune to the issue.
I did not try to be confusing in my explanation, but apparently was. Please excuse me if I got too long winded and hard to follow.
By the way, I have never tracked the manufacturer of oil filters I have changed over the last two decades, and have never seen this problem myself. Without any data that adds another brand, I think it is likely an issue with a batch of these things from this vendor. I will stop here as I do not want to monopolize the forum on this topic. Good luck and I am waiting for those photos! Jim
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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)
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