Hi,

I have lost both of my rear door lock Knobs.... it seems that they just pull of fairly easy! Now I have both rear doors with the metal pin popping out and it looks cheap!!

Is this a common problem?

Also have been looking and cant find a place to buy the OEM replacement from... Any one knows where to look for an OEM replacement?

 

hmmmm....I don't think this has ever happened to anyone else....

First off, since you look to be new, welcome to the forum. Secondly, use the search function. I think every single rear lock pin on every single 2008 W204 has been replaced. Mine fell off without ever having a passenger in the back.
Obviously the dealer will replace them for you.
If you want to get away from those beautiful little black plastic pins, there are a lot of replacement options the will screw onto the fronts but the rears have a pressure type lock and will have to be more or less custom installed.

 

Common problem that has been discussed in length many times. You can get them replaced under warrenty but they will break again. Do a search for door pin to see others solutions