Not quite up and running yet.... I recently took the front wheel back to Hagon to have them check it for run-out and spoke tension now I'm putting the bike back to solo use. It'll be interesting to see how the solo bike handles with the 19" wheel.
As for the stem - yes, I'm going to progress looking into an answer as to why the three 'cracks' have occurred. In the first instance I'll contact the place I did my m/c C&G courses a while ago, Merton College in SW London. They should, I hope, be able to point me in the right direction if their own material science dept can't deal with it. I really want to get to the bottom of it and won't rest easy until I have answers from those who know more about such matters than me! I'll update here as and when there's any new info.