I have always bled the brakes after changing pads or shoes. Technically, Shark is right. If you do not open the brake system to the environment, it is not required. Some people may not have an area where they can bleed the brakes, but could change pads without alarming someone. However, we all know the amount of dirt and moisture that collects in the brake fluid. This dirt and moisture will eventually corrode the inside of flex lines, steel lines, calipers and wheel cylinders. It may be overkill for some people, but it takes a little extra time and ensures that clean fluid is in the system where it counts. I am always amazed at the color of the fluid that comes out. Unfortunately, most vehicle owners never get their brake systems flushed, especially in these economic times.

 

I used a piece of small clear Plastic Tubing. Just pushed it on the end of the Bleeder and the other end in a old Antifreeze Jug to catch the bad stuff as it came out.

Like you, I've blead some systems that I was sure never had been opened since new. Brake Fluid can certainly...either go bad, or really get discolored without any influence except use and temperature. If it's not really clear, I want it out of there !

 

I also use the old pad and a big C-clamp to push the piston back in.

The fluid closest to the brake does eventually wear out, you can actually boil brake fluid.

I'd say the next pad change, at 140k, I will bleed out the brakes.