I am a retired North Pacific commercial fisherman and currently farming(livestock and hay). I also have a small stable of W123 diesels either restored or under restoration. I have Three 4wd tractors. All the tractors I have owned and the commercial fishboat engines as well as the gensets have had both primary and secondary filters and some have filter screens like the MB diesels. Our fishboat engines used Racor fuel filters made by Parker. They are not cheap. Almost our whole fleet used them. Racor makes replacement filters in sizes from 30 microns down to 2 micron media. They have large clear plastic bowls and a water drain as well as heating elements and pressure gauges.. Some are very large as were our boat engines. The fuel available in BUSH communities is often old and contaminated with debris, algae and water and having an engine quit in stormy conditions in the Gulf of Alaska can be fatal . I always added 2 micron filtration as the final filter before the injection pumps. The point of this post is to suggest adding improved filtration to 240 and 300D engines to extend the pump and injector life of these aging diesels. I think the MB filters do an adequate job if serviced regularly and I have read their micron specifications as high as 20 and as low as 6 microns from company websites. In my experience there is no such thing as fuel that is too clean and filtering down to a few microns is desirable. Obviously too fine a filtration will lead to restricted supply if placed as a primary filter. Once I place my 2 micron filters as the final filter I rarely have had to change them. We change our filters based upon fuel pressure monitoring. The upstream filters are the ones we service which are of course Racors. The fuel lines on the MB diesels with their hard plastic and banjo terminations are an obvious problem and so far I haven't placed 2 micron filters as filters before the IP. I have placed a 5 micron Racor filter just after the plastic screen filter in my 240D. Here is my suggestion to lead off to this discussion. Why not add a 1 or 2 micron filter on the return line to the tank? Great access with just hose clamps before the cigar hose. My other suggestion is to install a "fuel polishing" system which we also used on my last big boat. This is an electric pump constantly circulating fuel from the tank through a 2 micron filter. In our boat we ran it 24/7 during the season as a way to watch fuel quality since we sometimes pumped fuel from rusty drums on shore. We mounted it by the helm so we could always spot trouble ASAP and we had a vacuum gauge set to a light and bell alarm to alert us if the tank fuel was problematic. These are the 2 options I am considering. The return line filter is certainly the easiest but I do not know how much fuel flow returns to the tank and whether it is ample enough to do much good. Anyone out there with Ideas on this project? BTW, Baldwin and CAT make 2 micron filters for use on big rigs beside Racor. I should also mention that we put hard hours on our tractors in frequently dusty conditions and I regard fuel and air filtration as well as frequent oil changes as mandatory maintenance. Our tractors also have fine micron by pass oil filters. They run flawlessly and I have yet to service the pumps or injectors.