Using epoxy to hold the glass itself in place would be a bad choice, as the thermal expansion of the glass is different than the surrounding materials - this is why a clip is used rather than a more secure solution. The clip allows movement.
If you can figure out how it was originally attached, and repair that (perhaps with the aid of a welding and/or machine shop then that would be the ideal solution.
However, using epoxy to hold wire or a metal clip of your own design in place that holds the glass in place would also work out well enough.
Note: If the item that was holding the glass in place was rusted/damaged enough that it no longer serves its function, chances are very good that the heat exchanger is also nearing the end of its life, or already has pin holes, which would allow combustion gasses to enter the building. Do a thorough inspection.
Is it DIYable? Yes. No. Maybe?
You may find that you start the job, everything works out just right, and you complete the work in record time and under budget. More likely, you'll run into a bunch of unforeseen problems, take 5 times as long as you'd expect, and end up way over budget.
The best way to tackle DIY work that you are not sure about, is to have the resources available to quickly fix mistakes. In your situation, it might be a good idea to purchase a replacement window before you begin. If you damage the old window beyond repair, you'll simply have to install the new one. On the other hand, if the repair works out, you can return the new window you purchased.
It also never hurts to have somebody with knowledge in the type of work you're doing, so if you run into trouble they can offer guidance.
If you come across something you are really not comfortable with, there are always professionals available to do the work for you. You might also be surprised that they charge less than you might think (not always the case, but does happen).
This window lock is broken and I don't know what tool to use to replace the lock. It's just round hole, not a screw. I can't even identify the window manufacturer. Any help?
Best Answer
I am going to guess this picture is taken looking down onto the top of the lower sash of a double hung window? The wood I see at the bottom of the picture is the wood flooring a number of feet lower? If so you can drill out the pop rivets on both halves of the sash lock and replace both halves with a new unit that resembles yours as close a possible. They are available at a hardware store. You will need a pop rivet gun to reset the locks in the same way, but you may need to drill new mounting holes too if the new lock has a different spacing for the mounting holes.