The problem is that there are so many contaminant sources and the viscosity of those contaminants vary so greatly that unless you know the potential culprit it is difficult. You need the ICP of each one in order to try to identify the contaminant. After that if you can compare the viscosity of that compared to the new fluid you can then estimate the percent contamination. All easy said unless you have more than one contaminant. Water is the easy one.
Am I helping this or just adding to the confusion?
My definition of an expert in any field is a person who knows enough about what's really going on to be scared.
~ PJ Plauger