Hi Cigar Havana,
it is 11 NM or about 8 ft lbs (as per MB CD) for my '87 420. I assume it's the same for an '89.
There are 2 nuts on top of two bolts, which hold a bracket I believe for the AC on the driverside. You have to loosen these nuts, otherwise the bolt will snap when you loosen it. Yes, it happened to me.
I hope you have a better calibrated torque wrench than I had. Once you see the gasket split, you know it's too much torque. Mine was calibrated afterwards...