I work next door to a plumbing supplier who is also open to the public. In
his opinion, any faucet under $600 is junk and won't last more than a few
years. Really he said that. That appears to be your case though.

Go to a plumbing supply house to get your insert replaced, and talk with
them about your other problems, they'll be able to help more than a hardware
store. Otherwise you might have to bite the bullet and get a plumber.

S