There have been upgrades, but they do not work well in the older motors. Stick with the old copper plugs your manual calls for, do not get the new bosch platinum plugs that the store will try to sell you.

Didn't mean to imply you were an idiot. Issue has been discussed here fairly often, and everyone agrees that sticking with the OM's original recommendation is the only way to go.

__________________
'90 300SE 298k
-300K and it gets put into retirement.
'80 300D 255k Purchased new by family in 1980.

Had a:
1973 220 (gas)
1980 300SD
1992 400E