The coil still may be bad even if the resistance is within range. That is not a reliable way of testing.
My wife's car, a 1989 300e, has 135k miles on it. It was having a slight rough idle problem, a slight lack of power, and would sometimes take two tries to start in the morning. Other than that, the engine ran fine.
The cap, rotor, plugs, and wires (from dealer) had been replaced 15k miles ago. So I just changed the plugs last week (Bosch H9DCO). Car ran a little bit better.
I thought the coil may be going out since it was the original unit. Instead of an OEM unit, I replaced it with an Accel "Electronic Super Coil". The Accel is a higher output with 45,000 volts. The idle has improved to a point that sometimes it is hard to tell if it is running or not. The car fires up in the morning immediately. Power is back to what it should be. My wife, who knows nothing about cars, asked me what I did to the car because it now runs great!
The Accel coil fits perfectly where the original was, on the lower side of ABS mounting bracket. You may need to drill a few mounting holes, but I made a metal bracket to allow me to use the existing mounting holes. The coil is about $50 mailorder from Jeg's.
I ordered a new cap and rotor from FastLane and will replace that this weekend just to top things off.
So for $50 buck and about the same amount of work as testing the coil, you can have a new high output coil. It made a big improvement for me. You will have to modify the coil to distributor wire. Accel provides a 8.8mm coil wire, but I just modified the existing coil wire to fit on the Accel.