On two separate cars (both German VAG) I have removed a caliper (or two) and not connected the brake line again before the day after, and when I bleed the brakes it never gets back to it’s old self. I have tried both a vacuum bleeder connected to caliper and a pressure bleeder from the reservoir, and it doesn’t work, brakes still squishy. So I guess air has creeped up through the system to the master cylinder while the system was open over night? How do I bleed my master brake cylinder?