Some commented " what do manufacturers know " and the answer to that, would be, " what they have been told by cleaning machine manufacturers "
On a private tour of a carpet making plant, accompanied by the head of quality control, we paused at the Q/C area, where newly woven carpets were visually checked.
When soiling was spotted ( oil spots, dripped from machines ) the Q/A boss, demonstrated how they were dealt with.
A tin about the size of an average tea cup with a simple, soft bristle brush was handed over. The brush was immersed in the tin which contained solvent , the brush was shaken, to dispense with excess solvent, then applied to the oil with a rapid, light brushing action, so the soiling was not removed, but dispersed, over a larger area.
This was the standard procedure and had been for decades, apparently.