Brake Drum Wheel Cylinder problems of the 2014 Buick Encore

My girlfriends 2014 Buick Encore with about 15,000 suddenly had the brake pedal go "spongy". Twice at intersections while holding the brake pedal down it would suddenly drop about 1/2" lower. Also while sitting at a stop with the engine running it became possible to continually push on the brake pedal until it reached the floor. Her 2014 Encore has only about 5000 miles of in town driving with the rest of the mileage being highway. The local Buick dealer (bachrodt in rockford ill) noticed a small drop in the brake fluid level level, but dismissed this drop and the pedal change to "normal brake wear" and would do nothing to fix the problem. Upon taking it to the Buick dealer (anthony Buick) in gurnee ill for inspection, that dealer found a "leaking master brake cylinder" and replaced it under warranty. Had I not "forced the issue" and taken the car 45miles away for a 2nd opinion, we would have been stuck with a car driving with a leaky master brake cylinder until it failed and caused an accident. It is also interesting to note that the replacement "part number" of the master brake cylinder has changed from when the car was new in November of 2014. A photo of the service record showing the brake cylinder is attached.