Fresh from my local car boot sale a Glunz roll film camera, 120 film and 6 x 9 cm in fairly poor cosmetic condition. On the front face of the shutter area it says 'Original Gaultier', on the shutter setting dial it says 'Pronto' the speeds are 'T' 'B' and 100, 50 and 25.
The f numbers are 4.5, 6.3, 9, 12.5, 18, 25, 36. Unfortunately I think that the front element of the lens is missing, though I am not sure. I cannot get the back open, although the catch moves. I have done some research on it and it was made in Hannover, probably in the 1920's by G. Glunz & Sohn Kamerawerk.
Yes..... it does look like the front element is missing, the lens would have been 105mm F4.5, or perhaps 120mm as it is 6x9. The chance of finding a front element are low, maybe another cameras lens would fit along with the back elements, the sizes were not standardised, but were made to fit the bought in shutters. A similar shutter and lens night be fitted to the front standard, I don't think the Glunz name is on the shutter.
The cameras made by Glunz are middle of the road in design and quality, like several makers they lost sales in the late twenties and went out of business. Most of their early output were plate cameras, with pretty standard designs.
On the back catch, it is clearly a simple two claw slide, so give it a soak in thin oil, or WD40. You can dilute thicker oil with paraffin to thin it. This should free the slide, but the back can be glued in by rust or corrosion, so carefully pry the edge open when you can the catch claws are in line with the slots. Slide a sharp knife blade along each slot around the body to free it, and then thicker blades till it gives. It looks like an aluminium body, and aluminium oxide may have formed in the joints. The oxide expands when forming and seals the gaps. In the worst cases it is a white powder, which really jams things tight. Nothing will dissolve it, it must be scraped away etc. With a steel case it will be rust, and that dissolves with Phosphoric acid, which is easily available and relatively safe, it is used for flux for soldering and as rust preventer.