It sounds to me like you have a sticking caliper piston or restricted brake flex hose. The act of the brakes dragging then causes the brake fluid to boil causing reduced braking on both front wheels.
Please don't tell me that you are taking a Mercedes to a brake shop. I presume that is what a "Speedy" is. Even though they may be very competent in their trade, they very often have poor parts purchasing capabilities and they aren't used to working on 20-30 year old cars that still work. They tend to overkill everything. Not to say it won't be needed with an old car. Its just that experience is a money saver here.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
[This message has been edited by stevebfl (edited 03-16-2000).]