One thing I did notice about the 4400 with the optional filter was that I had a lot of crud in the bottom of the oil pan. I had to scrape it out with a gasket scraper.
I think I will refer to this crud as 'inert dirt' because, if I had to scrape it out, it seems unlikely that oil flow would have moved it, unless you went to a kerosene purge, or some additive.
