Thanks, but I'm not sure how air can get into a closed system and the brake fluid was replaced/flushed with pressure to pass through the ABS. So, this brake fluid is less than 6 months old and brakes were fine after this procedure was done for a few months.
Maybe this will be of some help. Have you ever replaced the brake hoses? They break down as they get older and get weaker.
They can expand under pressure which may cause your pedal to get mushy. Also use a flashlight and look for any weeping of brake fluid around the connections of the hoses and the calipers.