I have an Amscope ME300TZ-2L-3M metallurgical microscope. While investigating possible causes for poor picture quality and cleaning the optics, I discovered that the mirror was not appropriately fixed to its mount and, in fact, fell off. I glued it back with cyanoacrylate.
After that, I’ve realized that I have a box with a disassembled Pentax *ist DS2 camera, so I’ve removed the mirror from the mirror assembly, heated it at approx. 180 °C to soften the rubber (apparently silicone) glue attaching it to the mirror mount, scraped off the glue with a fingernail, and attached it to the microscope mirror mount. For that I had to, first, remove the original mirror using a heat gun at approx. 280 °C, which made the cyanoacrylate viscoelastic but (predictably) broke the mirror in the process, and second, file down one part of the mirror mount, as while the Pentax mirror is nearly identical in dimensions to the original mirror, it is slightly wider and slightly shorter.
The new mirror performs slightly better than the old one, with a small but noticeable reduction in glare, likely due to the different coating. The overall function of the microscope is not significantly affected.