Rust repair or panel replacement?

Repair when the surrounding metal is sound and the corroded area is smaller than a hand span. Replace the panel when corrosion crosses a structural seam or when more than about a third of the panel is affected.

Rules that hold up:

- Cut back to bright, sound metal. If you can dent it with a screwdriver, it goes. - Butt-weld repair sections rather than lapping them; laps trap moisture and rust again from the inside. - Prime the inside faces before you close a box section, and use cavity wax afterwards. - Never rely on filler over a weld seam more than a couple of millimetres deep.

Ask any bodyshop to show you photos of their work at bare-metal stage. Finished cars tell you nothing.