This old thread is place to brain unload a 96 S500 W140 m119 water pump change for searchers. 280,000 miles, car started wavy temp needle. Changed thermostat, water pump and temp sensor, ok. Remove serpentine belt and water pump pulley.

Water pump was changed without removing fan or harmonic balancer. Forum people have stated there is a "early" solid harmonic balancer disc, and a "later" spoked disc.
My 96 has a spoked disc and, thus, the bottom middle water pump bolt could be removed by a ratchet/extension through the disc opening. A solid disc would be a problem.

Remove upper hose manifold that has the lifting eye from top of water pump. Remove the thermostat from the side of the water pump. The lower 10mm bolt is hard to get at, removed with 1/4-inch ratchet and extension. Buy magnetic socket inserts, helpful for this. You will probably ruin the 90 degree thermostat hose, buy one.

The water pump is held on with 8 bolts. There are different lengths, keep track. The upper right bolt comes in contact with the harmonic balancer, by just a mm but will not slide out. i had to cut the 13mm head off with a Dremel and use a 80mm replacement bolt with an Allen head to go back. The lower left bolt goes through the fan pedestal foot bolt hole that sits over the water pump bolt hole. This pedestal is not readily removed. I removed the bolt and the water pump wriggled out from the pedestal foot OK. The problem is going back in with the new pump. With the new gasket tacked to the engine, the gasket slides over when sliding the pump in the tight space. More space is needed. The water pump aluminum of this bolt hole on mine was 20mm. I filed 1mm from the backside, and it slid in OK for the bolt to go through the pedestal hole, the water pump hole and the gasket OK. All other bolts are no issue. When tightening down the pump to 15 ft-lbs, remember there is a 1mm gap on the lower left bolt. I cut a 1mm washer in half and slid it in the space as a shim. Went OK.