No, another person responded my mail.

Hi Pierre,
I had the chance to open a friend's defective M3Z in standard configuration.

I found out the (4) phillips headed screws from the top side hold the 2 visible lenses to the housing.
The slotted (5) screws hold the 2 guiding rods of the zoom sliders.
So there is no chance to open the ...

Thank you, Pierre!
Merci beaucoup!

I slided 3 drills into the holes, found the locking position, slided them in to the stop, locked internal ring and turned the gear wheel counter clockwise.

M3Z_holes.jpg

There was a slight friction that decreased a bit while turning.
I turned about 10 turns counter clockwise, but friction didn't ...

This morning I found 3 small holes at the white gear wheel.

M3Z_1_of_3_holes.jpg

When I slided in a thin 1,5mm drill and turned the gear wheel, I found 3 positions (each 120°) the drill could be slided in a few extra millimeters - and the gear wheel was some kind of "locked".
So, I thought ...

PierreH a écrit :It will be hard to remove this black part

I've removed one of the grey epoxy seals by the soldering iron method. But there is no screw, my assumption was wrong.
I see no accessible screw nor possibly hidden screws I could accesss from the outside of the microscope...

PierreH a écrit :good luck!

Thank you.

I've marked the epoxied areas in red.
I've also marked the areas I suggest the long screws you mentioned, in blue.

M3Z_hidden_screws.jpg

I'm not quite clear how to remove the epoxy.
Maybe I use a hot soldering iron...

PS: The reason, why I want to remove the unused parts:
I want to have access ...

You have to remove the black rectangular part to see these 2 screws...
Thank you for your reply!
I've tried before to remove the black rectangular part without success. I'll try again to find any screw behind.
I think the big white gear-wheel is bolted to the black triangular plate, but then ...