I've had the same thing, and due to some recent questions, I also got some photos of the last one.
If your drum is similar to this, there may be a reasonably easy way:
This one was split on both sides, as seems typical of all those I've seen. I unstrung the tuner, removed the drum, removed the cord tension spring (which has to be flipped to allow the hook to pass through the slot), and opened the split very slightly. Guessing that drum was molded in ABS, I used solvent cleaner liberally and in multiple passes to fully clean the opened area, but also to soften the plastic in preparation for solvent cement welding. Once it had been cleaned at least four times and was still somewhat soft, I applied ABS solvent cement to the opened crack, then opened and closed the crack several times to help the cement wick into the openings. After a final application of cement, the crack was allowed to close, and I assured its closure with a small spring clamp. Allowing the cement to dry for several hours (overnight) I removed the clamp, applied additional solvent cleaner, and topped the entire repair with additional solvent cement. Another several hours of cure passed before the drum was installed, and careful tightening of the set screw secured it to the VC shaft. When it became apparent that the split was not going to open again, I removed the drum, restrung it, tensioned the dial cord on the spring, and installed it.
ABS solvent cleaner/primer and ABS solvent cement are commonly available in small containers intended to solvent weld ABS pipe. Be certain to use only ABS cement, and not a PVC, CPVC, or universal solvent cement. Sufficient time to cure is critical, so this cannot be hurried unless you want to wait the appropriate amount of time the SECOND time you have to repair it.
The first time I did this I was prepared with some ABS welding rod to cover the area completely, but.never had to since the solvent welding has held up.