One problem related to brake fluid leak has been reported for the 2005 Chevrolet Avalanche. The most recently reported issues are listed below.
Stepped on the brakes to stop for a stop sign at a major intersection and my brake pedal was good a first then completely sunk to the floor. The truck stopped in the middle of the intersection that was thankfully void of traffic. My wife and I were a bit shook up. It could easily been worse. We carefully traveled to the nearest service station and were lucky to get flatbedded to a local Chevrolet dealer. Memorial day 4pm in georgia, I did not have high hopes. The service people examined the truck and it was apparent that my truck had catastrophic failure of the brake lines. I thought it was a master cylinder due to the complete loss of fluid. While we waited for tow truck I purchased brake fluid and filled my completely empty reservoir, had my wife step on the brake as I watched the fluid just pour out from the front drivers side area near the frame.