I went the entire factory replacement route on my 1993 400E about 10 years ago when I bought it. I thought I wanted to do it right. Mercedes sells the wire by the meter and I think the ignition wire is actually a different diameter than the plug wires. I bought the crimping tool too. If you get the tool, when you insert the caps on the ends of the wires, pay attention that the threaded stems are hollow and there is a smaller crimping device on the tool so you can crimp the threaded stem at the base after you've inserted the bare wire into it. Be careful not to bend the stem. You will also crimp the collar of the caps around the outside of the wire after that--a more intuitive application of the tool. If you didn't know any better, you might miss the fact that the threaded stems need to be crimped too. Believe me, it's easy to do. (You would probably notice it, though, when you tried to screw the caps into the boots and the wire pulls out.)

I'm not really sure the wires are like domestic cars where they lose resistance over time, but, at the time, I just presumed they were the same as my 1992 Camaro Z-28 with headers, where I always have to throw a new set of solid core, high-heat Moroso wires on every 30,000 miles. Anyone with experience here may be able to chime in. I too am interested in whether anyone has found the wires themselves to go bad. Arthur Dalton suggested in a prior post that the boots go bad before the wires do. In the past 10 years, I have only changed the resistance boots that go over the plugs.

In any case, both ends will screw off the wire with some WD-40. I would try the boots first. It may save you some money. The whole thing with wires, distributor caps rotors and the tool was well over $1,000 from the dealer and that was a decade ago.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles