I have seen this many times on the 103. Usually the head will come off and have a complete valve job and oven treatment to straighten. Then the water pump is done with the head off of the car. (Many times easier to get off.) Flush the coolant system with some water and a whole bottle of shout.
You should be fine.
1981 280GE SWB
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM