The upper molding pieces are available from parts dealers in the US (MB might have original spec molding but at twice the cost of reproduction pieces.).
Even the repro molding is quite costly, about $100 to $200 each piece. High cost could be the reason we see that a fair number of cars being sold are missing the rear pieces on the back fender.
The molding can be held on with Pop Rivets, or screws and plastic Mollys.
Echoing Naj's suggestion, new molding insert is the way to go, A lot easier than trying to revive dried out rubber. New insert material (enough for the entire car) is only about $20.
Richard M, New York City