I had one of these last year,leaking water cooler that had been leaking for ages.
Although the carpet,blue office type,cleaned up like new,there was a permanent black watermark around the edge,nothing would shift it.
I put it down to molecular change,similar to plant pot stains,if it won't come out,it won't come out.
I totally agree that you should look after those that look after you,most of our work is on recommendation,and that is how it should be.John