Lexol is sold in Mercedes dealerships ...
It is acknoledged as the product which will replace the oils which dry out with the least darkening of the leather long term. But it needs to be put on more often as a result.

The Haynes manual has good pictures... but lacks some detail ...many auto stores carry the generic 123 manual

The Factory Shop Manual S can't be beat for amount of knowledge...but are clearly translations which are hard to decipher many times... But they do include the specs...and the fact that most items on the engine have three iterations...from Ebay....
And they are good about safety warnings...