Dot 3 brake fluid is generally what was used in our older cars. Dot 3 is very corrosive so you should be careful not to spill any on the paint.
Since the fluid was low, you should look for the source of the leak. Most of the time, it's the wheel cylinders that go bad. Look for wet spots on the brake drums or tires. Also look at the master cylinder for wet spots along the firewall inside and out. Examine all the brake lines too, rubber and steel. You do not want to have a total brake system failure, it's not good for paint either.
John