The old cuckoo bellow tops will just snap off the tubes. The top of the tube will have some old glue stuck which has to be carefully taken off with a knife.
Just carefully scrape it off until it is smooth. This way it has a nice, flat surface for the new tops. You will new epoxy as well for the installation of the new tops.
Clear 5 minute epoxy mixes A with B and is great for this project. The regular epoxy is also fine. Any epoxy that dries fast will do the job. After all, it doesn't have to be anything fancy.
After scraping the tops smooth, the epoxy will adhere well. If old epoxy is leftover, the bumps will make the new tops not stick as well.
Installing new cuckoo bellow tops
Once the epoxy is on the tops, either place them upside down to dry or clamp them. Clamping them is the best, however if you do not have them then turning them upside down is the next option.
Most importantly, the bellows have to be able to open without resistance.
This means there needs to be a gap between the flap that closes of the bellow top and the front of the tube. If this small gap is not there, the bellow will jam on the side of the clock case upon opening.
The top needs to be in the exact position as the old one was. As a result, it will be able to blow air into the hole that is in the top of the tube. This is so it will not rub anything.