put six of these from my local autozone into my 1990 300e. Car ran fine for about 3 days then starting missing like crazy.

pulled the plugs and they were completed fouled. tried cleaning them w/ carb cleaner but didn't get good results. seems I was just about due for tune up time and when I pulled distrib cap and rotor they were worn (some corrosion) and I think the plats just couldn't hang.

I like the gentlemen's advice about the old tried and true fat copper plugs, just like a lawnmower. I'll let you know.