The symbols light on my 87 300E as well, so if a '90 lights, and an '87 lights, then maybe yours should as well.
I have never done this procedure, but an article in the Star magazine on installing Euro lights talked about removing that panel to install vac hoses and a Euro panel for a headlight level control, so I bet that is how you get to the bulb(s). The article says "...pull the headlight knob off it's shaft, and undo the 24 mm nut holding the panel; wiggle out the panel, left side first." So, if your brave, and trust the Star article, it looks like you have access to the bulbs (in theory). Let us know if this works - it is logical, but the path to ruin is paved in logic!
2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)
Click to see 87 300E