Honda Repair: brake pedal problem, brake master cylinder, honda accord

Question
1993 Honda Accord LX 4 door automatic transmission 2.2L 90K miles:

Right after 90K factory scheduled maintenance done, the brake pedal is working differently than before.  
It weak,Spongy and will sink while you stepping on for brake. Sometimes the brakes will still work fine, but they seem to have grown weak. It takes longer to stop, or suddenly you get less braking power when you apply the brakes. The pedal feel more squishy than usual.

How to inspect step by step and find out the reason and fix it? Hope to have the information soon. Thanks.

Answer
G., brake master cylinder. New brake fluid with a full bleed of the system. Brake booster could have damage and need to be replaced. Odd that after the 90K service this happens but, not uncommon. If you feel adventurous, inspect your brakes by removing your wheels and physically inspecting the areas for rocks, build up, etc. That could keep your brakes from working properly. Do your pads need to be replaced? Check it out and let me know...