The pin they are talking about may already be removed. It is used to keep the float from banging around in transportation. It goes through a small hole in the lower portion of the outer wall (not from the bottow but through the side).
Try slowly turning the sender end for end. If the float can be heard moving then the pin is already gone look for the small hole probably about 1.5mm dia.
BTW, the design of MB sending units has stabilized their readings by only allowing fuel to enter through that small hole. When removing the old unit one will notice that the fuel flows from this hole for some time. When cornering or traveling in hills that change the attitude of the tank, the readings stay stable as the fuel takes times to change levels inside the tube. It is this vent hole that the pin would be in, if it were there. If you aren't sure remove your old sender and watch where the fuel comes from it.
Bosch Master, ASE Master, L1
33 years MB technician