What can be repaired
Minor lifting, small splits, or flashing that's come loose from its fixing but is otherwise sound can usually be re-dressed, re-secured or patched rather than replaced outright.
When repair is the right call
If the lead itself is in good condition and the issue is isolated — a section that's worked loose, say — repair is a sensible, proportionate fix rather than unnecessary full replacement.
When we'd recommend replacement instead
If we find the lead is thin, cracked in multiple places, or corroded, we'll say so honestly rather than patching something that's likely to fail again within a year.