Hi there, Edmund and Andrew,
Thank you for your posts.
Edmund: I'd be very grateful to see some photos of your centre punch in its dis-assembled state but I hope that it'll still be working once you've re-assembled it! I'd hate to have it on my conscience if it didn't survive the experience!!
Andrew: I'll take mine to pieces again and examine the back end of the point.
I bought this centre punch as a back-up but my main one seems to have gone into hiding!