I have just about finished with my water pump replacement on my 190e 2.6. It was not that easy being my first 103 water pump, at least I got it out myself and put the new one in. The two inner 13mm water pump fasteners were a nightmare. You can barely see them let alone crack them loose. I ended up with a 13mm 1/4in drive with a 6 in extension on the bottom inner fastener and 3/8 drive 13mm with a 6 in extension with a universal joint on the upper fastener. I used about 8 windings of electrical tape on the unbiversal joint to hold it steady while i crakedd it loose. Once loose they came right out. The outer lower was a piece of cake, but the 6mm hex inner upper fastener was very stubborn. The allen wrench wanted to take a walk. I eventually cracked it loose by using a 6mm allen socket and held the socket in the fastener with a lug wrench and turn the 6mm socket with the closed end of a 6mm combination wrench with a cheater bar. I also had a problem with the 5mm allen that holds the tube that gooes into the water pump that threads into the timing cover. These items would not come loose. I had to exert pressure to keep the allen key from walking out of the fastener.
The water pump went back together very easily thank the Lord. I am wating for my idler pulley, disributoe and rotor from Parts Shop so it is a done deal.

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1990 190E 2.6
1996 Grand Voyager 3.3
1985 Mustang GT 5.0 5 SPD
1982 Suzuki GS 750T