Differential wear and rust from water contamination
Here we have four examples of differentials where water entered through the oil seals or vents leaving dirt and wear or corrosion.
The first two samples are both from a Toyota HiLux pickup, both front and rear differentials.
The first sample still has 3.8% water content. This is accompanied by 67 ppm of potassium, 27 ppm of sodium and 243 ppm of dirt. The wear and corrosion is 572 ppm of iron and 41 ppm of copper.