Depends on the model for Cats. The old Cat 280/290 was a pump we could put 8,000 hours on before a rebuild, the 3cp goes about 600 hours.
Not had good luck with Hydrocells or Hypros, and the Cat 3cp and 5cps have not been much more reliable. At least the Hys are cheap to rebuild. By the time you buy the high heat kit for a cp and install it, you may as well just throw the old one out and buy a new one.
I talked to the Cat rep at the last Connections, and he told me that I should expect to rebuild a pump once a year. (!) But then he said Cats are great and the only reason they fail is the way they're used. (!)
We're in the process of changing out Cats and going to the new General
Emperor HTX. It's an expensive pump, but if it saves one rebuild (or catastrophic failure) it will pay for itself.