Sorry to hear your capper broke, you're surely not the first or last one. They aren't made to withstand the test of use and time, the head being plastic.
If you're handy, or have a handy nephew or cousin, you may be able to glue it back together with JB weld, then reinforce the stress areas with some metal plates, steel strapping, more JB Weld and a few small bolts in strategically placed areas.
While that may help you out for the time being, and may last longer than the original, I would start looking around for an all-metal steel bench capper. Even a flea market or CraigsList find of such is probably going to outlast you and your grandkids.
They do still sell all metal ones, for a price, but chances are crucial parts, such as the head, are cast aluminum or some composite/alloy, giving similar problems over time.