R&R'ing the M119's waterpump isn't too difficult, if you have the proper tools (pulley counter-hold; reverse torx socket for updated tensioner; (2) 3-ft. prybars; and 1/4-drive sockets/wrench) and a good/accurate and small torque-wrench (I have a Mountz 1/4"-drive that reads 0-30 Nm in quarter Nm increments).

Here are some caveats/tips:

1) clean the front of the engine with a good engine degreaser;
2) use a THIN coating of Hylomar sealant on all gaskets;
3) clean with a bronze wire-wheel and rinse with brake cleaner ALL bolts;
4) use high-temp anti-seize on all bolts (steel) that go into aluminum;
5) you do NOT need to remove the radiator, just the viscous-fan/clutch assembly and shroud;
6) you do NOT need to remove the lower alternator bolt, just loosen it;
7) if you do NOT have a pulley-holder, use an air-ratchet to loosen the waterpump and idler pulley bolts (NOT tensioner pulley) with the serpentine belt still on (acts as a counter hold);
8) use different colored paint on the bolts to keep track of them and write-down the key/legend;
9) turn the crankshaft bolt (CLOCKWISE ONLY) to TDC and mark with paint the orientation/location of the following: pulley to harmonic dampener; harmonic dampener to cranshaft bolt);
10) soak the CENTER of the harmonic damper to crankshaft bolt with Aero Kroil; PB Blaster, or a good quality penetrant, preferably overnight;
11) you do NOT need to remove the crankshaft bolt (400Nm) to remove the dampener;
12) remove the dampener using TWO 3-ft pry-bars (left & right side) by gently wigglying out the dampener and being careful where you brace the pry-bar for leverage;
12) gently clean the mating surface of the engine block to waterpump with a bronze wire-wheel and wipe-down with brake-cleaner and number the bolts;
13) REPLACE the thermostat (clean all hose connectors and mating surfaces);
14) place a rag under the REAR thermostat housing's bolt so if it drops, it doesn't go into never-land and have spare M6-20mm bolts;
15) use anti-seize on the thermostat cover bolts and NOTE only 10-Nm on these;
16) use a heat gun on LOW or a hair-dryer to "soften" the water-pump's weep-hole pipe and then gently tug off the waterpump and use the same heat source to "soften" the pipe when re-installing;
17) remove the pipe and tank (one bolt) to make dissassembly easier;
18) when replacing the idler-pully bracket, keep the bolts with enough slack since you have to align/bolt-up back the airpump; alternator AND bracket back to the block;
19) when replacing the thermostat elbow hose, smear a little hylomar on the metal hose housings to facilitate moving/bending the hose into place;
20) REPLACE the hose between the thermostat TOP housing and INTAKE and the gasket (thin film of hylomar)
21) DO NOT OVERTIGHTEN esp. with antiseize on bolts and into aluminum. Most bolts are 21 Nm, but with antiseize on them, it's closer to 12-15 Nm. Do NOT use a 3/8-drive ratchet to put any bolts ON, only 1/4-drive with about a 5-inch long handle so I don't overly torque anything.

BTW: I use a vaccuum-based coolant installer that basically uses the compressed-air to create a vaccuum in the cooling system, and then by flipping a valve, I suck in my 70% distilled water and 30% G05/Mercedes coolant with Redline Water-wetter.

Hope this helps!

:-) neil
1988 E36T AMG
1993 500E