Sounds like a lot is going on.
The fluid is probably getting hot because the rotors are either warped or the wheel bearings are worn out.
Id upgrade to late model brakes because the early model brakes always get hot and consequently squeak (at least for me).
It is possible that your wheel sensors are bad which would cause the problems under 15mph.
So Check your wheel bearings, check to see the run out of your rotors too. Then go from there.
Do a flush of the brake fluid when you do all this work, its probably bad from being hot so much.
No Benzes in the stable at the moment, but itching for one again.
Former Mercedes in the Stable:
1983 300CD Turbo diesel 515k mi sold
1984 300CD Turbo Diesel 150 k mi sold
1982 300D Turbo Diesel 225 sold
1987 300D Turbo Diesel 255k mi sold
1988 300 CE AMG Hammer 15k mi sold
1986 300E Amg Hammer 88k mi sold
1992 500E 156k mi sold