Rear brake pads and rotors were replaced and the car seemed to drive and brake perfect for the first day. One day later I notice an intermittent "pulsing" when I apply pressure to the brake pedal. Sometimes it is more noticeable than other times but took it back to the shop to diagnose. Mechanic "reset the system" (sorry I don't specifically know what this means) and we drove it and again we are feeling the pulsing of the brakes upon pressure to the brake pedal. It seems more apparent when driving at highway speeds and braking. It sort of feels like the pulsing an ABS system makes in the rain for example.
When the rear brakes were replaced there was no need to bleed because the hoses were not disconnected but bled the brakes anyway and same issue. Next put a new set of pads and rotors on the front and the problem is now gone..
Is this all coincidental or does anyone have any ideas about this?

Some background on the car..
Initially the car went to the shop for a intermittent hard starting issue which was fixed by installing a new camshaft position sensor and crankshaft position sensor. This is when the mechanic noticed the rear brakes were almost shot..

About two years and one month prior the car was in the shop for the same hard starting issue at which time the same two sensors mentioned above were replaced. Luckily my mechanic was able to get one of the sensors warrantied and the other one got a 50% break on. Do these things just go out every two years

Around the same time also had to replace the entire transmission and radiator due to the presence of glycol in the transmission. No help from MB

Also one of the air suspension components in the rear of the car makes an annoying "thump" sound occasionally going over bumps.. I've been told this is not affecting the functionality or safety of the car so been holding off so far on this repair.

One other thing I almost forgot is about 9 months ago was out of town in this car and brakes went completely out while driving- that's right- pedal to the floor and zero braking. Luckily was on a city street going slow and was able to pull over safely. Car was towed to shop. You guessed it-- SBC pump. Another big FU from MB- they refuse to cover any portion of it. Thanks

I purchased the car with 40K miles in 2012, I am the second owner.

So far in my ownership of this car it has been a complete POS compared to all the other MB's I have owned in the past.. Sorry for the rant folks and I appreciate your insight.

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05 E55
03 E500