if theres not a key hole then its probably a small button in the car otherwise you just pull it open.
in front of left hand side rear wheel under a cover
Buy a Hayne's manual for the Mercedes diesel or a Chilton's manual for Mercedes (it has a 123 Mercedes on the cover). It will show you how to change the inline fuel filter and the main fuel filter.
The fuel filter on my 1999 E320 is located on the drivers side just in front of the rear tire. There is a plastic cover with 3 plastic nuts; remove those and you will see the filter. DominicArnold@cox.net
Mounted on top and inside the fuel tank.
1999 mercedes ml 430 translator pump Hoses leaking
On the passenger side in front of the rear wheel. It is cover with a black cover. Remove it and there is the fuel filter along with the two fuel pumps.
Under the car RHS under a plastic cover with four screws. it is an external fuel pump.
the fuel filter is on the side of the rear passenger seat in front of the gas tank. you have to remove a plastic cover to get to it.
The fuel filter is under the car you have to remover the plastic cover under the car to get to the fuel filter.
get it in eBay ,,Mercedes w208 CLK 320 clk430 Fuel vapor recovery Valve,, its 73.90$+shiping8.10$ need to replaces Wat i found and that's what I'm gonna do this weekend.
It is under the chassis in front of the rear right wheel cover with a plaastic shield and it´s with the fuel filter.