Getting inside is straight forward.
Start by removing the foot. This is held on by two screws.
Once you've removed the foot you reveal the single screw that's holding the back on. Remove this.
You can then slide the back sideways a bit....
.... and then move it towards you to remove it.
With that out of the way it's back to the bottom of the M330C to remove the screw that's holding the cover in place.
With the screw out you can then slide the cover back and lift it off
This is the only time where you might wonder whether you're doing the right thing!
The cover, at least my cover, is a good interference fit and it takes a little effort
to shift it. It moves back about 9mm to clear the lugs at which point you can lift it off.
Any comments? email me. Added May 2016