I am coming up to 24 months on brake fluid on a Mercedes and decided I would test it with a brake fluid test strip, the one that measures contamination. Since it was my last test strip, I cut it in half. I got a reading of zero. Not only is this unusual in itself, but even more so because I tested the same brake fluid a month or so after it was put in and got a very slight reading of about 10 which made sense. So I took the other half of the test strip and put it in my other car which I had done a brake fluid exchange on 8 months ago. I got a reading of 30. This made complete sense since a reading of 200 requires a change and we're not heavy on the brakes. Are the corrosion inhibitors in genuine Mercedes fluid that good that after 19 months there is no corrosion being picked up? Seeing they suggest a 24 month change interval, could it be because of moisture fears rather than contamination?