Fancied having a go at changing the 16 plugs on my SL55 and saving the £300 plus I've been quoted by Mercedes. I've taken four out so far, and the threads have all been coated in this sticky goo - I assume this is to stop the corrosion I have heard about. So my question is, what is this goo ? What do Mercedes recommend using ? Will ordinary high temp MS3 castrol grease be OK ? That is what I have available. Other than that, this is an easy enough job, and highly recommended.