Engine oil

[Bob Culver]

The late VW Beetle with no filter, usually little consumption, changed at 3,000, but did have a magnet and air cleaner, and more used than typical Seven. With typical Seven use condensation and acids more likely significant than dirt.
The oil has to be well agitated  to suspend any larger material. Car can be rocked. The impecunious can pour oil through a filter and reuse!