You know there's 5.1 also available which is glycol based and not silicone? Glycol is far more forgiving than silicone based fluids. It's also easier to tell if a glycol based fluid has been contaminated than a synthetic one. In fact DOT5 is widely stated to be more corrosive because of this fact and unless frequent fluid changes are done it's in fact worse for the system. About the only advantage I see of DOT5 is the fact it's paint-friendly.
