brakes hissing at pedal, pedal to the floor, no stopping power at slower speeds, no brake fluid loss. did the 3 step booster test it passed. I'm thinking just the seal between booster plate and firewall. is that a possibility?
Hissing from the booster is the rear seal. I'm not aware of anybody that sells just that seal. Plus, you have to remove the master cylinder and booster to disassemble the booster just to install the seal, so it makes no sense. If the pedal goes to the floor with no braking, then you've got a problem with the master cylinder