As the other poster stated, I would love to know what fluid was being used. I have a couple Koolance Vid 280 full cover blocks (they have anodized aluminum tops) in my loop, and I have always used fluid with anti corrosives. I just pulled the loop apart to put in some bitspower 90's and 45's and decided to pull apart my full cover blocks and they look pristine, as does everything else in my loop. This is over a year of running on either feser fluid, and the last 6 months on distilled with pentosin.

I like the Vid 280 blocks, but the anodized aluminum tops makes me worry when I see a thread like this. I wonder how hard it would be to make a delrin or acrylic top for my blocks?