I actually have firsthand experience with Monark plugs. Hell, the same one's in that "kit" you purchased. I did purchase this kit myself a few months ago. I will give it this; they worked beautifully and made the car so much nicer to start when cold.

HOWEVER, please note the word "worked".

2 failed almost instantly on the 1 month mark. I did a full diagnosis of the GP system and the only plausible cause was a premature failure. I still have the plugs sitting around; they're brittle. Not very good....I'm really lucky they didn't snap on me. I immediately bought some Bosch large-bore plugs from Pelican and they've worked flawlessly for the past few months. And in the much colder weather to boot! I can't imagine those Monarks in weather like this...

TL;DR, These "opinions" against Monarks that people rant about have much credibility to them. The fact is they make a shoddy plug.

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- 1979 W123 240D 4-speed, 390k miles