Bottom, there are only two screws there, countersunk one, very close to m3 in size. But I'm not sure if it is m3, so I don't want to force m3 in there, incase it's some imperial size.
I have tried to read the service manual, hoping that things like that was specified, but couldn't find it
I bought mine from that UK seller that was selling huge amounts of these for some time ago. After trying to open it that time, and the screw was rusted, so I didn't dare to try again.
But I got this lefthand drill bits, and drilled the screw out, and I was suprised of how nice the unit was inside, superclean, no dust at all, no sign at all of caps leaking, or anything, so It seems I was lucky with my unit.
I tried to screw a m3 nut on the screw, but it feels like it's not quite there, so I thought it could be an imperial size, but I'm not so know of those sizes, so I didn't want to force it.