That was the surprise I found when I popped the hood at the last oil change. Got on the phone right then and ordered a replacement from the local dealer. Then, called a national brake repair chain and found out that a brake fluid flush would run about $50. When I took it in, they checked the moisture content of the fluid and found it to be within acceptable tolerance. So, as a precaution, they siphoned the fluid out of the master cylinder and refilled it. Looks like I "dodged the bullet" this time.