Another thing that can help with the intermittant bulb outages: use a round wire brush on the socket before using the dielectric paste.
A brush similar to a battery post cleaner does wonders at taking off any oxidation in the socket and helps get a positive connection between the bulb and socket.
Applying the dielectric paste helps to keep from having it oxidize again.

on my 00 e430, i do have the dash cluster giving a warning that a lamp is out, however I've already checked all the bulbs and they work fine.
should i still take out the bulbs in the rear and clean up the surfaces ?
is that what's causing it ?

It could be those plates, yes. But as you've read here, be sure to check the license lights, the cneter stop light, the fog lights, and the amber lights on the sides of the front bumper and the small clear ovals next to the headlights.
Gilly