Braking system is comprised of
- master cylinder
- brakelines
- abs system
- brakes
Do your brakes feel solid? any pedal movement (read: mushy)
I would check for the following..
- cracked/loose master cylinder cap
- loose bleeder valves at the brakes (this is why I asked about pedal feel)
- craked hoses between the two..
Other than that.. I wouldn't know where to suggest.. You have to have some slow leaks somewhere..
Ray