if it were my car, I'd start with the easiest to check: Go to the trunk and twist the holders on the right tail light assembly and check each of the bulbs. Twist them out; look for corrosion and blown bulbs.
Next I would check the right front turn signal marker assembly. Do the same process above.
Then I would check the license plate illumination bulbs.
If these do not yield anything then I would recall whether I used the headlamp cleaning unit at all during this time .... if not, I would by-pass it for now.
The remaining items can start to get more complicated ....
If you need to replace bulb(s), only use quality bulbs. Auto parts stores often have them on racks under the heading of OEM replacement lamps and bulbs. They are almost always made of silver looking metal. Do not waste your time or money buying cheap bulbs.
Try the above and let us know.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)