Have u (or has the previous owner) changed the OVP since u owned the car?

It is a square top, about 3-4 inches long, has a couple of fuses on top. The old one may have only one fuse.

It sits behind the battery, shielded by a plastic guard. Remove the plastic guard behind the battery and u will see a bunch of components back there.

If u r not sure which component it is, go look at one at the dealer, or better still buy one and u will know which to replace.

Mercedes has updated this component a few times after the original design. The dealer should have the latest. I would not go to anyone else as they be trying to offload the old inventory.

Hope this solves ur problem.