Folder "mtklog" on SDcard keeps getting full
After a while, and no valid answers, I have come up with the following workaround. The required steps are:


Have "Android Terminal Emulator" app installed, with busybox commands also installed (as described in question)
Make a list and check the folders that bother you. The list I've provided contains only files that I'm sure my phone won't need.
Create a bash script (.sh extension) with remove commands on that specific folders. Here is mine:


#!system/bin/sh
rm -rf /sdcard/mtklog
rm -f /data/log_other_mode/*
rm -f /data/core/*.zip
rm -rf /sdcard/DCIM/.thumbnails



Place this script on an accessible folder. I've chosen mine to be /system/etc just as a convenience related to chmod'ing and such. And because unfortunately the sd-card is always mounted with "noexec" which means that you can't execute anything from here.
If you are not able to do so, it may be because your system folders are mounted as read-only. To change that, you need to do the following command in the terminal:


mount -o rw,remount,rw /system


and to revert it back to read-only:

mount -o ro,remount,ro /system


Note: You probably will need super-user (sudo) privileges in order to do these commands.


The terminal emulator contains an "Widget" option which allows you to place a shortcut to a command in your phone home page. I've used that option with the following command: 


su -c /system/etc/scriptName.sh; exit


Every once in a while I click on this icon to make a clean. This asks permission for the user, since it contains a su command. When clicking "allow" the terminal finishes and closes automatically.


It's not an optimal solution since it needs the phone to be rooted, and you have to manually click the widget button. However, it was the best one for me, since making it run automatically would require it to ask for permission. I didn't want also to give the terminal emulator permanent access to su-privileges. My guess is that a more complex script can be made (e.g. one that monitors the size of the folders with the Disk-Usage command), but I'm happy as it is.