What sparkplug for 89 300se

Have found Bosch RD 971's in car. Wrong plug or replacement to ones listed in owners manual?

[1991300SEL]

BOSCH H9DC0

Manual calls for a gap of what amts. to .032

Many claim they get a smoother idle going higher - some as high as .040. I set mine at .036.

There is also an H9DC, but it's electrode is not quite as wide as the H9DCO. I've used both and cannot see a performance difference.