Morris Mini-Minor

On the classic Mini the corrosion sits on structural parts, and the buying guides list it in one breath: the A-panels at the wing/door joint, the front and rear subframes and their structural mounting points, the floors, inner and outer sills, the front wings and headlamp surrounds, the boot floor and battery box, and the door bottoms. Rear subframe towers inside the boot corrode from condensation, and floors rot under carpets where door and windscreen seals have perished. Because the subframes carry the suspension and steering, corrosion there changes handling and can fail an inspection — and a car that looks straight on the road often hides a rotten subframe under the paint it was restored with.

The A-series engine is the weak link in every classic Morris, and the 1275cc unit introduced in 1964 ran its bore around the maximum the block allowed with very little metal between the middle cylinders — a design compromise that often contributed to head gasket failures. In the Mini the problem is amplified by the layout: the gearbox shares the engine's oil, so a failed gasket or an overheated engine contaminates both, and the tell-tale is an emulsion on the filler cap. Head gasket failure on an overheated A-series is one of the most common expensive faults, and it usually means pulling the head and having the block and head professionally checked for straightness.

The Mini's four-speed sits underneath the engine and both run in the same oil, which is a triumph of packaging and the reason gearbox wear is so normal on these cars. Worn synchromesh and a rattly box are described as common but rebuildable, and the classic symptom is baulking or crunch on second gear; the wear is accelerated by owners who never change the oil, since the gearbox bath picks up metal from both units. Because the box is bolted to the bottom of the engine, a rebuild means dropping the whole unit out, which is what pushes the labour cost above the parts cost and makes service history worth more than a shiny engine bay.