My trusted mechanic at one of our local Mercedes dealerships replaced the 250SL's front discs and callipers this spring. Driving back from the dealership to my home, the brakes suddenly became soft and I could push the pedal almost to the metal. I stopped, the car was taken back to the dealer on a flatbed trailer. By the time it was unloaded, the brakes working fine again. They kept the Pagoda and the service manager (an older German man, familiar with these cars) test drove the car a few times and could not find any problem. I drove the car home a week later and drove it quite regularly during the summer. No similar issues came up, but the brakes lack the same bite I was used to on the old set. Last weekend , the same problem came up again. The service manager suggests that I may want to replace the brake booster, but there was no issue prior to the replacement, so I am hesitant. Any ideas would be appreciated.