OK, finally an update from my side.
The BNCs for channels 1 and 2 have finally been swapped.
After putting the repair aside as it wasn't really necessary to fix and I didn't have time, I approached it again.
I finally was able to make sense of the descriptions in the service manual.
As for the sequence of disassembly: After removing the case, you proceed to remove the CRT bezel. Undo two screws and take it off.
This also releases the catch on the front cover of the storage and horizontal module. This again can then be removed by undoing the centre screw at the back.
Be careful, as there are a few wires going to the horizontal deflection plates and to the HV power supply.
After that remove the power supply sections. A lot of screws and even more connectors have to be undone.
Take notes of the connections! Not all are easily found in the schematics.
With the power supply removed you can proceed to remove the acquisition board. First thing that has to go is the shielding. After that you desolder all connections around it and take it off.
You'll also have to remove the cam shaft for vertical DIV adjustment.
After all that you can now remove the metal piece that holds all the BNCs.
For details see the photos. If you want to try it yourself, get in touch.
(Photos not in sequence)