I just repaired the relay in my wife's 98' C280.

To be specific about the relay location;

After you remove the carpeted truck liner, there is a large black plastic cover towards the front of the car. It is about 2 feet by 3 feet, and is held in place by three large head plastic screws, which you should be able to remove with your fingers.

Lift off that cover then locate the relay toward the right, it's easy to see and is positioned horizontally. It is the only relay that I could find under this large cover (there is another relay under a small black box, that can be accessed without removing the large black plastic cover)

Once the relay is removed, I used two knifes to pry the sides away from the relay bottom to slip off the relay cover.

I only found one, possibly two locations with cracked solder, I fixed them both of course. I didn't remove the old solder however, I simply heated up the bit that was cracked until fluid, and then added a small amount of thin resin core solder to blend in.

I realize that this isn't the way explained in other post, but I'm confident it will be adequate in this situation.