The $0.99 Bosch Super.
I use 'em in all my vehicles.
Put some in my 280e (M110) 5K mi. ago and they're still pristine white.
Car starts.
Hauls ass.
They work great.
I also have a plug cleaning machine.
Great for restoring fouled plugs.
Saves money and trips to the store when adjusting mix.

SDS
1980 280e (M110)117K mi.
1980 450sel silver 200K mi.?
1980 450sel blue 210K mi.