Ever since RealVNC updated VNC to version 5.0, CCleaner has not been cleaning VNCViewer's MRU list. After some investigation, I have determined the cause.
In version 4.0, the MRU location was:
HKEY_CURRENT_USER\Software\RealVNC\VNCViewer4\MRU
In version 5.0, the MRU location has changed to:
HKEY_CURRENT_USER\Software\RealVNC\vncviewer\MRU
Please update VNCViewer4 or add VNCViewer5 to the list of Applications.
Thank you