Don't know? Here are the facts: Regular DOT3 fluid can absorb tremendous amounts of moisture. This moisture will rust out the area applied rather quickly (hours) if it is applied to an area where bare metal is exposed. Not only that, but DOT 3 is terribly damaging to ordinary car finishes, especially today's weaker, more environmentally friendly types. This is best done on a humid day, or light rain, so that it resembles rain on the hood, roof, etc. A few days later, "why is my car/SUV still wet there? And it's rusting!" Ohhhh.. too bad Bob, that's going to be expensive, isn't it?
As far as the application, get a cheap spray bottle, and remove the filter on the bottom of the pick up hose (the thing that is in the bottle, bottom of cap) for added power. It is a bit messy, but the satisfaction is worth it. Wear a coat you dont like much on the days you spray. You dont necessarily HAVE to scratch the surface first, the DOT 3 brake fluid will still do quite a number on the paint. Guaranteed. I accidentally spilled some on my car, and it ruined the paint. Have fun!!!