I sounds like they found the right code, but not the right resistor end. On the 104 engine, there is a tell tell sign to look for. You have to pull the plugs and keep them in order. You will be looking for the plug(s) that have a streak on them. I have seen this over and over. I a plug or plugs has the streak, replace that respective end and clear the codes, (assuming the coil is OK) ...9 times out of ten it is just the end.
Clear codes and all is well.
There is not a really good way to scope this engine, so the tech may be guessing unless he knows this trick.
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS