This fuel filter is a factory replacement for your 03-06 Mercedes E55. The factory does not sell a replacement filter but rather wants to sell you the entire housing assembly at a much higher cost.
Filters are lower micron then the factory filter which help protect not only your injectors but your engine as well. Replacement intervals need to be more frequent as the filter is trapping more particles then factory filter. Filter may have residue on housing from gluing in o-ring, we do not consider this a defect, only cosmetic.