How to restore missing space in C:/ Drive when updating The Sims 3?

I have a 500GB C:/ drive, i installed The Sims 3 on the D:/Drive.

In installing the expansions (starting from World Adventures and so on...), the windows installer pops in, prompts me to do an update first (which is needed in order to install the expansion), i clicked yes. Did this for succeeding expansions - But this ate up a large amount of space in my C:/drive successively. From 315GB (i started with, before installing Sims 3 base game) it went down to 276GB (39GB worth of space for patches??? - after installing Sims 3 + Expansions) 

I tried finding the actual files itself manually in the C:/drive - no luck (with view hidden files and folders turned on)

I tried locating the files with WinDirStat (a tool that shows file size allocation) to no avail - it doesn't show/list the files. The only biggest allocation, it shows is the Windows Folder @ 20GB. 

My %temp% folder is less than this (88MB)
My C:/windows/installer is only 2GB
Tried defragging, tried CCleaner. - Both didn't free up so much space

Note: i did not install anything else big in between, i just installed ONLY Sims 3 and Expansions all the way and recorded/noted the large drop of C:/drive from 315GB to 276GB, then stopped installing since i noticed the huge space consumption on the C:/drive. (And yes, i did check that the actual program files are installed in the D:/drive, not the C:/drive)

What's causing the C:/drive to lose so much space if i can't find the file?