Say the front of the oil filler neck is towards the radiator. Look in the back between the neck and the valve cover and you will see a stop that won't let you turn counterclowise. Well, you have to turn counterclockwise. Pull up the back of the filler until past the stop, then turn counterclockwise. It will come right off. If you turn clockwise, it will spring back in place and won't come off.

To insert the new one, just turn clockwise until past the stop, it will then spring back in place.

Actually in my case, after buying the new filler neck, I just cleaned up the old one, turn the gasket backwards, and inserted back in place. No leaks since. I have 2 benz that use the very same part so I just kept the new one in case I need it again.

Looks like it is a common problem because I went to a little bitty MB stealer we have on the west side of the city and even them will have it in stock.

You bet.

Rene