Just finished replacing the water pump on my '86 300E. Took me about ten hours which also included replacement of the belt tensioner, all hoses, thermostat, and belt. I took my time and removed/cleaned many parts (radiator, fan, pulleys, etc.) while I had access.

Thanks to the tips in this forum I knew what I to expect and saved a ton of money.

I used a Sears Craftsman 13mm flex socket to get to the notorious water pump bolts. The most difficult part was not getting access but loosening the bolts which required an air wrench.