Check your bulbs against what is spec for your car. I believe the specs are listed in the back of your owners manual.
Some after market bulbs do not work well with Mercedes. Cars with the bulb failure system on the dash often have problems with incorrect bulbs.
Try checking the tail light clusters. These seem to be subject to moisture and are easy to check.
Keep us posted,
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)