DOT 5 is silicon-based fluid. Unless you've replaced your entire brake system, never use it - it reacts VERY badly with residual glycol-based fluid. Among other things, the remaining glycol fluid will suck up water and form little pockets of spongy fluid that will compress at a different rate than the silicon fluid around it. When glycol fluid soaks water normally, it will spread it fairly evenly throughout the system.
Also, from AAA web site:
"Silicone DOT 5 fluid has some other characteristics that you should beware of. Silicone fluid compresses slightly under pressure, which can cause a slightly spongy brake pedal feel. Silicone fluid also attracts air more than polyglycol fluid does, which makes brake bleeding harder. It also tends to vaporize slightly just below its boiling point; and it will aerate from prolonged vibration. All of these factors mean that DOT 5 silicone fluid should never be used in an antilock brake system."
Good enough?
[RICHR]