Ask the mechanic/technician to return all the parts to you. If you should need one of these parts in the future, replacements might not be available, such as the master cylinder, wheel cylinder, or caliper, but rebuilding will still be available. This is only one reason to save the old parts. The master cylinder is specific to the commercial chassis and has the lines facing the center of the car to differentiate it from a passenger car. They both look the same, but internally the valving is different. I had a difficult time sourcing one for my 1969 Commercial Chassis, and even finding a rebuild kit presented a problem. If you need the rear axle seals I have a few pairs that I saved for when I got a 1970s Commercial Chassis Car.