if its brown gel is probably a colony of some bacteria or something, truckers in EU have been infected with legionaires disease, their most common trait was using plain water in the windsheild reservoir tank, the spray mist gets sucked into the vent and into the cab.
Thats why a bit of alcohol is used.
If you feel its not cleaning up, remove it from the car, (yes I know its a long job on that car) but thats the only way to clean it.