Does anyone have experience with excessive vacuum in their crankcase as evidence by suction on the oil filler cap? How much is too much? Is any too much? In searching YouTube it looks like its caused by a bad Engine Crankcase Vent Valve 2760100331. Does the oil separator drip pan, 2730100162 also play a role in the problem? My ML350 has 135K miles. It runs rough when cold but once warmed up its fine. The vacuum on the cap is always there.
Thank You.

 

I replaced the crankcase vent valve PCV. The suction on the oil filler cap is still strong by seems to be a little less. Attached are pictures of the insides of the vent valve.