Replace front rotors and calipers with rebuilt calipers. Find new shops to do the work; the old ones don't know what they're doing. My suspicion would be the calipers are hanging up due to drag on the pins or the piston inside. The rotor is being heated up by one or both and then when you put the brakes on you feel the warped rotor. Sometimes the caliper releases and moves away from the rotor and the problem doesn't occur noticeably; other times it is hot and warped. Use quality replacement rotors. My pick would be Raybestos rotors from Advance Auto available by mail order--not in the stores. I believe they were about $50 each--free shipping.
These cars are also very sensitive to out-of-balance and out-of-round tires. Fnd somewhere that has a road force balancer to do your balancing. They can also move the tire on the rim to let their out of round balance out each other. This was what was done when the cars were new. Many tires don't roll round when the weight is on them; they crush more in one part than another so the wheel goes up and down slightly just like an out-of-balance wheel. Michelins tend to be the best for being round and staying round when they roll. Related chasses to the one you have used Michelins from the factory or replacements under warranty to help reduce the problem with the stiff chassis and light weight alloy suspension parts.