replace all of it, otherwise it will contaminate the new fluid
No.
Yes. You can fix the mistake of putting engine oil in the brake fluid. It is the easiest if you just caught it as soon as you did it. In that case you disconnect the master cylinder as quick as possible from the brake lines. You do not want oil to clog the brake lines. Then you remove as much brake fluid, oil mix from the master cylinder as possible. Then you take a rag and clean out the master cylinder. Then you run brake fluid through the master cylinder until it comes clean. Then you run brake fluid through the brake lines to make sure they are clean. If brake fluid does not go through the brake lines, you did not catch it in time. You need to replace your brake lines and slave cylinders. You have just learned an expensive lesson.
yes because brake fluid wont wear out as much No, brake fluid will destroy the seals in the power steering system.
A few reasons. Fluid has a much higher density, and makes it easier to apply more force to the brakes. Fluid is much easier to contain and refill. No special equipment is necessary to fill a brake fluid reservoir.
nothing
brake fluid absorbs moisture thus brings the boiling point of your brake fluid down to a much lower temperature. if your brake fluid reaches this temperature you can loose your brakes temporally. also the moisture in the fluid will cause highly unwanted corrosion of internal parts of your brake system.
there is too much in the container If you filled the resevior with brake fluid PRIOR to replacing any of the brake linings, it will cause the fluid to "backflow" into the resevior, thus it will overflow and leak from the cap.
How much does it cost to replace brake pads on a 1999 Mercedes Clk?
Might depend on HOW MUCH brake fluid you put in there, but not much. The radiator holds quite a lot of mostly water, so a dash of brake fluid will quickly become very diluted. But since the radiator doesn't expect brake fluid, it'd make sense to have it flushed and refilled as soon as possible.
until the first line
If you are looking for more information on how much does it cost to replace brake pads, the best place to look for the information is on ask.metafilter.com/39783/A-reasonable-price-for-a-brake-job
Before you add brake fluid, are you SURE you need to add some? Because as brake pads wear, the brake fluid level goes down, but the brake pads need to be replaced then, BEFORE any brake fluid is added. Otherwise, when the brake pads ARE replaced, there will be too much brake fluid in the reservoir, and it will flow out when the pistons are pushed back into it's bore, to make room for the new pads. -Tom.