When was the last time the brake fluid was changed? Brake fluid absorbs moisture from the air and that changes the brake fluid dynamics over time. Also, it allows air pockets to form within the brake system, which is what I believe is leading to the spongy feel. The air pocket will compress, the brake fluid is designed not to. Changing the brake fluid every 3 years eliminates these bad effects. If the fluid has never been changed, now would be a good time to do it.