Stop driving/running it.
This requires direct hands on diagnosis.
You need a good local MB specialty shop for this issue.
Good MB Shops
http://www.peachparts.com/shopforum/good-mb-shops/
* It is possible the pressure sensor is bad = repair could cost $50.00 - $200.00 USD.
* The bearings and/or oil pump may be failing = repair could cost $1300.00 - $8000.00 USD.
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