help,dont know what to do 420 sel

[Louis]

I bought a 86 420 sel around 2500 miles ago, after reading this great forum, I decided to replace the spark plugs. I posted a topic on what plugs to use. The previous owner had bosch platinum 4 in the car. I was directed by most of you to get rid of them right away and run the bosch super (wr9dc). After doing so the car ran bad i.e rough idle and missing. I put the platinum's back in and it seems to be running great again. My local parts house told me that the valves had set themselves to only run with theese plugs because of the extra firing of the platinum 4's, but this is bad because I have aluminum heads and that the platinum 4's will ruin my valves because theese plugs run real hot. Please any help would be great. this is my first MB and I wish to keep it.