I'm a bit confused about the choice of spark plugs for my 280 se 3.5 L.

At the moment it runs well on Beru 14 8 DU (equivalent to Bosch W8DC ...I believe) but the time has come for my first general tune-up.

In reading some of the past postings for a 4.5L, it was recomended to use the Bosch W7DC plugs. Firstly are the spec requirements the same in both motors in the ignition department (i.e. spark plug gaps and contact point gaps, etc)? Secondly, the question of hot plugs and cold plugs - why would hot plugs be used? The Beru 14 7 DU (~Bosch W7DC) is recommended by one MB spare parts dealer then another recommends Bosch W9DC. The current plugs used falls in the middle of the two. Which one of the three should I choose?

Please note I only use 98 octane unleaded with fuel additive for the valves lubrication because Tobias runs really well on it. The standard fuel just makes the engine run noisier and a lot less power.

Now spark plug gaps. The MB CD says it should be 0.5mm but past posts advise 0.028 which is 0.7mm. The current gap on the plugs being used is 0.7mm. Should I just stick with 0.7mm?

Looking forward to your advice.