I've read many posts on the fix for intermittently working cruise control to replace the brake light bulbs as a first cheap fix without going to the module. My questions is: Are you guys replacing them even when they are working fine? Is the cruise control that sensitive to slight degradation of the bulb? I've also read that as long as the bulbs are of good quality and new, it doesn't have to be Mercedes OEM bulbs, what's you experience out there? I guess the one way to make sure they are of good quality is to get the OEM bulbs... Thanks,

That one has been floating around for years. If the bulbs work, they work...that's it. The cruise control ECU gets a ground signal through the bulb filaments. The bulb tale used to be even more elaborate claiming that the incorrect bulbs would "fry" the cruise box. I only use OEM Osram bulbs. But it's because I LIKE them...no other reason.
Typical ECU failure is a system that will work in the accelerate mode but doesn't hold. Or one that drops out of cruise frequently. I have repaired a few by re-soldering connections on the circuit board that looked different from the others.
Regards,
Randy D.