So some months ago i picked up a fery clean 98 e300. Had some other issues that were more pressing. When i looked at it, it had a very soft to the floor brake pedal. But the brakes did kinda sorta work. Was low on my list and asked the seller. Told me he swapped pads and used a c clamp like usual to compress the piston. Afterwards the pedal was aweful. Well once i finally started working on the brakes i looked up the procedure. Says that it required a power bleeder at 2bar to unseat the abs check valves. Conventional methods could damage the master. So i hooked up the motive bleeder and worked my way around. Got the fronts to spit, rears remained a dribble. Also noticed the rear fluid was really dark and back part of the master was dark. End result brakes were better but pedal still drifted.

Decided to replace the master with a TRW master, bench bleed first and installed. Got a better look at the rear circuit. Had some sort of sludge or really dirty. This time had my pops in car, set the bleeder to 2 bar. Had him pump along with bleeder. Rock hard pedal. Again the rears spit a little tiny bit, if i had him pump under pressure nothing spectactular. The fronts, with the bleeder open under pressure every pump was halthy stream. After a while i notice i had frozen rear calpier. After finished had a so so pedal, that would go nice and hard with a second pump.

Next step was today, replaced both rear calipers. Bleed the brakes under pressure key off, key on engine off and engine running. This time after many pumps i could get the rear to spit one time then dribble. The fronts stayed working as they did.

Took it for a test drive, firm pedal with emergency stop. A normal planned stop pedal firms up after about 20% of throw. Rock hard after a double pump. Low speed driving, soft press and goes down.

After reading some various stuff and talking to mercedes tech. One article said had to activate the abs with scanner. Saw another saying similar problem had crap in the abs circuit. Mercedes tech said only use oemmaster cylinders and he never had an issue like this. I was thinking maybe the rear hoses are coming aprt inside after 195K?

Any one have any input.