I'm pleased to say my little bit of Ebay business earlier this week has apparently fixed the problem with the Corsa's headlights. There was some shenanigans this morning when I first fitted it, and I spent half the morning fiddling about with the stalk that is in bits and pieces on my desk (I now know how it all fits back together, but some springs make it practically impossible to do), but I just nipped out again to check something, decided to give it a bit of a clean and it now works just about perfectly. Fingers crossed it stays that way!