A couple of weeks ago, I just happened to notice that my brakes felt different. When coming to a stop, the brake pedal would start pulsating. It wasn't warped rotors as I know how that feels. The brakes were pulsating as if the ABS were actuating after hard braking. It also was harder to stop as I almost rear-ended another car twice. Plus, the brake hold feature was also not operable. I couldn't figure out what the problem was so I brought it to a Benz dealership to diagnose. They told me that it was the brake booster and master cylinder. After getting the estimate of $4500, I drove it home and looked for a brake booster. I found a used one on eBay part number A1664301230L. The one that was on my GL63 was A1664300530 but discontinued.

It was pretty simple to remove the booster. You don't have to remove the wiper assembly but you have to remove the master cylinder and booster as separate units. The master cylinder just has 2 bolts that attach to the booster then remove the brake lines. There is also a wiring connection you will need to remove. Remove the vacuum hose and the valve. For the booster, it's just 2 bolts on the interior of the firewall at the brake pedal and the bolt that connects the booster to the pedal itself. Disconnect the wiring harness connected to the booster. You will have to go under the dash push in the brake plunger arm towards the engine compartment and rotate the booster. Wiggle the booster out. You wont need to remove the wiper arms. Install new booster. Bleed brakes.

Testing the booster is fairly simple. Just figure out a way to pull vacuum to the booster. You can do this with the booster still in the vehicle. If it doesn't hold a vacuum, it's done. What I did was use the tube that connected to the booster and use a vacuum pump and gauge.

My booster failed at just about 200k miles.