AC Compressor Bearing or Oil?

[YuCrew]

On a 1999 ML430 with 165,000 I have what I can only describe as bearing "rumble". AC cools fine, clutch engages and disengages as commanded.

1. Since the noise is present with the ac on or off, I thought it was the clutch bearing so I replaced it. Noise still there.

2. I did notice a very little bit of oil under the compressor (compressor oil leak?). What is the process to remove the oil and refill to proper level?

3. "Rumble" is not noticeable at start-up or during the first few minutes of engine warm-up.

4. Once warm, the rumble is most noticeable when in gear but stopped like at a traffic light (gear being drive that is...have not checked other gears).

5. If I load the PS pump by turning wheel to either direction (from half turn to full lock) and hold the wheel there, the rumble quiets down. I suppose the belt load on the compressor is also increasing somewhat.

6. I thought it might be PS pump but using the very scientific "stick to ear" method, placing the stick on the PS pump, alternator, near idler or on tensioner, I hear nothing alarming (car in gear, wife thankfully standing on the brake). When I place the stick on the compressor, it is noticeably different, distinct and I'm fairly confident the source of my problem.

Is it possible I have a compressor bearing (not the clutch bearing) issue? Can the compressor be re-built with a new bearing? Any other thoughts besides replacing the compressor (easy to do except for the environmentally responsible refrigerant "re-capture" part of the replacement process)?

Could the noise be due to a failing Case bearing (item 15 on the attached exploded view) or simply lack of compressor oil?

Thanks a million for your inputs.