If you buy some modelling plasticard (ABS sheet) of around 1mm to 2mm thickness, you can easily make a rear cover for the F1G2.
It is nothing very complex and may be held in place using double sided tape at the edges or double sided foam tape in the middle. For a permanent attachment, the rear panel may be glued in place at the edges. Plasticard is easily cut with a scalpel and very versatile. It comes in black to match your cameras case but you can spray paint it with satin black or matt enamel paint to make it match better. Necessity is the mother of invention
![Wink ;)](https://www.eevblog.com/forum/Smileys/default/xwink.gif.pagespeed.ic.cldandycH0.png)
Sadly even faulty F1G2 cameras seem to sell for decent money as they contain the Lepton 3 core that is normally in perfect working order. I have not seen such a unit at a wallet friendly price for a long time. I own several that need repair but I hope to repair them or sell them as spares. Without a rear panel it devalues them greatly, sorry.
Fraser