A smart tip for when to replace a ballcock
While replacing only the seals of a ballcock is easier than replacing the entire unit, it's not always possible. It's not always easy to find replacement parts, and some were never meant to be serviced. Also, ballcock seats eventually wear out. In these cases you'll have to  replace the ballcock. Referably with a modern fill valve.

Previous:How to cleaning a mineral-clogged toilet?

Next:What is the stop-and-waste valves?