After I run CCleaner, I run Ad-Aware, and it always find 1 MRU, which seems CCleaner didnt find.
...\software\microsoft\windows media\wmsdk\general\{0}
Spybot-S&D also finds something related to WMSDK, however it's the same exact thing each and every time which is the reason why I don't even bother cleaning that reference anymore because it will automagically reappear on I think a system reboot.