I've got SSH access and have now deleted mionet and optware, but still have used up 96% of rootfs and looking through the logfile, I can't see where. Most of the data is in shares (61Gb) and according to the logfile only 107MB in usr, 2.7MB in bin, 3.3MB in lib, 134MB in var and very little in anything else.
rootfs 2.8G 2.5G 128M 96% /
/dev/root 2.8G 2.5G 128M 96% /
/dev/md3 950M 151M 751M 17% /var
/dev/sda4 455G 61G 394G 14% /shares/internal
So what on earth is taking up 2.5GB worth of data?
The MBWE 500GB has also been through the Rescue Procedure given here thanks to it failing to update with SSH out of the box.
Thanks to all those that helped and chorlton for pointing me in the direction of 'open file descriptor' error.
To fix the problem I reinstalled the firmware as per: Force Firmware Update
However, I realised after doing this the reason for the problem! I had tried copying data to the device following a rescue procedure(required to allow any updates at all!) without the shares/internal drive being mounted, though the web interface had allowed me to set up folder shares. Presumably these files and share folders had occupied the root partition, but weren't visibile to du. Perhaps going through windows to find the culprits might have worked, although it could have been very tedious!
Anyhoo, thanks for the help… good place this!