It is not uncommon for the power steering rack to develop a fluid leak requiring replacement of the rack assembly. Loss of power steering fluid may also cause an abnormal noise and damage to the power steering pump.Google+
Car Problem Reports
Mercedes-Benz ML350 Steering Rack Prone to Leaks
Mercedes-Benz ML350 Problem
Average Mileage: 81,350 mi (37,200 mi - 200,000 mi)
Visitor, 2008 Mercedes-Benz ML350, 54,000 mi
My 2008 ML350 has developed a very tight steering issue, especially when stopped or moving slowly. The driver can feel flat spots when trying to turn the wheel and the wheel is very difficult to turn. After a decent amount of driving time, it seems to ease up, but for shorter commutes the hard steering lasts the entire time.
Power steering fluid has been topped off but wasn't noticeably low when checked. This is a safty concern and it worries me that Mercedes is aware of this, due to the number of customer complaints, and has done nothing about this. Many of these vehicles are driven by females, namely mothers with children, and this problem should be looked into and a permanent repair should come from Mercedes.
Had to replace the power steering at 59000 miles. Just learned that there was a recall. I was never notified of this by the dealer since I did not own the vehicle when I they sent out notices. So aggravated and seeking recourse.
Visitor, 2007 Mercedes-Benz ML350, 59,000 mi
I can't believe it. I just paid off my car and now I have to deal with expensive repairs. This is my 2nd Mercedes. I will never buy another one again.
Visitor, 2004 Mercedes-Benz ML350, 200,000 mi
My car has been leaking power steering fluid since about 110,000 miles. I now constantly replace the fluid on a regular basis rather than paying the $1500 repair cost.
Just learned that my steering rack is leaking and needs to be replaced. $1500 for the parts plus $600 labor. Called Mercedes, they told me there is no recall on that.
Visitor, 2003 Mercedes-Benz ML350, 120,000 mi
Power steering leak replaced the unit holding fluid starting to leak 50,000 miles later or 2 years.
Visitor, 2004 Mercedes-Benz ML350, 78,422 mi
ML350 made winding sound when putting vehicle in motion. Sound would go away as vehicle sped up, but would return when slowing down at lights or to make turns. Discovered small leak of power steering fluid. First look it appears from the hose and not reservoir.
Noticed leakage on garage floor. Placed drip pan underneath and determined that leakage was power steering fluid. Took to dealer (7th MB, always take to dealer-better results). Dealer said probably steering rack. Options: 1) replace rack, ~$3,000 or 2) install "seal replacement kit", ~1,500. Plan to keep vehicle as has been bulletproof till now. Mech found leak where P/S fluid reservoir attaches to pump and resealed it. Brought home, cleaned garage floor and parked truck. Next day noticed more leakage. Back to dealer. Now mech finds leak at the input shaft on the steering rack, same options. Upon questioning mech says the dealer (small dealership) has done this replacement (option 2) several times and has had no come-back on it so I went with that. Job is labor intensive in that to remove steering rack, the front differential and a support member have to be removed and replaced. Obvious MB knows of this issue but haven't been able to find any MB tech bulletin on it.
Visitor, 2008 Mercedes-Benz ML350, 76,000 mi
Noise when car is cold with steering. Required new unit
Visitor, 2008 Mercedes-Benz ML350, 82,000 mi
First there was a whining noise when steering. Discovered the power steering fluid was low. Filled fluid to normal levels which stopped the noise, however a slow leak was remained. Apparently the leak was in the shaft and the whole thing had to be replaced at a price tag of $2729.25.