Thank you. The second scenario is the case. Yes will do it 18 months. Now, I bought a small pump that will suck the oil through the oil stick. Is that a good idea? It could be a nice, easy and clean job this way.
One more question for you what oil would you use for my Merc 2015 S350 bluetec? I know that Liqui Molly or Motul are the most popular brands but any suggestions are welcome and greatly appreciated.