1) 84 model year with aftermarket discs. may be able to take a lathe resurface? But new disc are the way to go, lots of MB shops have throw out their lathes.

2) first you have to make sure it's not a malfunctioning ABS, your car have ABS, which shouldn't be hard detect if that is the cause.

3) Your talking about noise and not feel so lateral runout of a disc when braking should cause some vibration, Is your thump thump just noise or do you feel it and where do you feel it? hands, seat

That car dosen't have rear drum brakes does it?