After a short journey, I noticed that the car was looking cross-eyed. The headlights had moved to point more inwards, and they could both be moved easily by hand, especially the offside one.

The adjustment is simple; loosen the lower nut, realign the light and re-tighten. Simple.

However, the lower nuts were significantly rusted onto a very fine thread and the usual soaking and heating methods to loosen them did not work 😞