Strange spots on parquet, where do they come from?

Hello everyone!

The stains shown by the OP do indeed look like stains from some kind of liquids.

I have a similar problem and have been wondering for several months what the reason for the "stains" on my parquet is.
Or rather, I know the reason itself, but not the cause or a clear explanation for it.

The stains = streaks on the parquet floor in my pictures come from the wheels of the drawers. The streaks are exactly where the wheel tracks are. But it has nothing to do with "abrasion" or similar. The wheels are made of solid rubber, but the weight of the drawers is relatively high.

The parquet (oak) is oiled by the manufacturer.
Could it be that, due to the weight, the oil is somehow "pressed out" or something similar?
I myself come up with no reasonable explanation or way to avoid the streaks.

Rollers that always run over the same spot on wood leave marks. This cannot be prevented. (unterschiedliches Rollenmaterial mehr oder weniger)

If the "streaks" are indeed related to the path constantly traveled by the rollers, the following procedure should be considered.
The following should be taken:
a) a soft hand brush
b) two lint-free wool or linen cloths,
c) denatured alcohol or ethanol
d) an oil/wax mixture suitable for the surface protection of parquet surfaces.
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Procedure (however, not suitable for "smoked" wood surfaces):
One of the wool cloths is laid out on a plate and thoroughly moistened with denatured alcohol or ethanol.
The hand brush is then dabbed onto the wool cloth soaked with ethanol so that the solvent still adheres to the bristles. (Background: only a very small, but sufficient amount of solvent is transferred to the parquet surface).
Using gentle circular motions, move the hand brush over the streak(s) and immediately clean the affected area with the second (dry) wool cloth.
Repeat the whole process possibly several times.
Finally, re-oil the cleaned area, let it soak in, and after 1 day, polish again with a fresh wool cloth.
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Background:
It is very likely that the streaks are dirt deposits, regardless of their nature.
A gentle solvent and also a softly acting mechanical action (via the hand brush) must be used during cleaning.
My advice does not guarantee success, but I believe it is a promising approach!
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This will be my last post in this group, as I will be leaving Germany permanently next week.
It has been a pleasure for many years to be able to "shed some light" on the way for one or another here in this specialist forum with my expertise in the field of floor technology and to contribute to solutions, or at least to further insights.
Regards to all forum participants:
KlaRa

oh, you are leaving soon? That is very unfortunate for the forum!
Still, all the best with what sounds like an adventure from what is read here. :)

It's a pity your posts were always very professional and well explained.

By the way, except for a few spots, there is internet everywhere in this world, often even better than in Germany.

Bye :(
But hopefully you know that you don't necessarily have to live in Germany to answer here? ;)