M-Class (W164) Produced 2006-2011: ML280CDI, ML320CDI, ML420CDI, ML350, ML500, ML550

ML350 Power Steering gets hard after warm-up on low RPM's

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Old Oct 26, 2022 | 09:07 PM
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w164 ML350 145K Miles
ML350 Power Steering gets hard after warm-up on low RPM's

Issue started as a hard PS turning (on low RPM) with whining noise on cold (backing-up from the garage) as well as after prolonged driving.
What I did:
1. Changed PS reservoir ("A-Premium" brand off Amazon)
2. Changed rubber gasket (OEM MBZ Dealer part)
3. Did PS bleeding by rotating lifted wheels 30+ times to both extremes with engine off
However when I started engine to finish the bleeding (reservoir cap off) in case PS liquid needs to be refilled, it shortly started foaming and overflowing.
Symptoms now:
PS is not hard when engine cold, but still with some whining noise. After some driving when car is warm, low RPM PS turning is very hard and whining noise is increased.
What I suspect (here I need your guys input/advise):
1. Hose or clamps have some leak (it is still original) - would explain foaming
2. PS pump is bad - car has 145K miles
3. Bleeding hasn't been done correctly - but heard that system bleeds itself after driving 30+ miles
Any advice greatly appreciated.
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