A while ago I put up a post about my brakes and the consensus was that it is the master cylinder that is bad. I was told that it could also be the booster on the other hand from other sources. So I'll tell you what the situation is and you can tell me your thoughts.

All the pads on my car a fine and the rotors are as well, the fronts rotors are almost up for replacement but not yet. There are no visible leaks in the system at the calipers and master cylinder and the fluid level has always stayed the same. The brakes have not been bled for at least a year. ABS works when it needs to. Pedal pressure is the same as its always been.

What happens is that at a stoplight the pedal slowly loses pressure and the car creeps foward. If I immediately pump the pedal it gets firm quickly and will normally hold, only sometimes will it lose pressure again. The pedal always feels firm, just looses pressure and falls to the floor.

From the search and reading past posts I'm fairly confident that it is the master cylinder, I just want to be sure. The only thing that I have heard about the booster going bad is that it creates a spongy feel which I don't have. So any thoughts?

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1992 Mercedes-Benz 400E
2002 Mercedes-Benz ML500