You can send the scum to me and I will look at it in the lab. A couple of other things to check. I would make sure the last step chemical injection is metering properly. Some truckmounts have check valves that prevent backup into the heat exchange system. I would look at that possibility as well. I would also double check my vacuum and psi.
There also can be wicking from backing. Remember that the Triexta fiber does not absorb water so any rinse will go deep into the carpet and backing so extra dry passes are important. I would lower my usual psi for these fibers. Flex Powder is great as breaking up oils so if loom oil is the issue then residuals of the pre-spray or rinse not vacuumed away could be wicking to the surface with some of this oil.
On a technical note clarified by my attendance to the
IICRC science conference this summer. I need to point out why cleaning with water only is invalid. The surface tension of water alone is around 70 dynes/cm. The surface energy of triexta is around 40 dyes/cm and for oils it is around 25 dynes/cm. The point is that the fiber is not properly wetting for efficient cleaning until the surface tension of the water is below the surface energy of the surface or soils. Heat helps as the surface tension of boiling water goes to 60 dynes/cm. Alkalinity or acidity do not change the surface tension. Solvents will drop it further but the volume necessary to make an impact is no longer possible under VOC laws. Most surfactants as low as .1% will drop the surface tension of water to a level where all surfaces we clean can be properly wetted. In short, water is incapable of properly wetting triexta fibers, let alone dissolving oils that love to bond to an oil loving fiber. In short, the water only cleaning method can be used (ignorance would be my primary reason) to move responsibility from the manufacturer to the cleaner.