The first time one of these broke i replaced the drum, the second time i decided to do something sensible about it.
If your printer has a broken gear every page will jam right after reaching the drum and when you open the panel and remove it you'll notice a bit of crumpling at the top. The picture of this object highlights the kind of damage you should go looking for.
The hole is intentionally tight, i just pushed it in but if you meet too much resistance you can widen it a little with a file. I printed it at 0.12 100% infill no supports.
The gear will likely fit other drum models as well.