Right, well, the clock seems to be running properly now, For the last few days it has been stopping after about twenty hours - I put this down to the dentition issue that I noticed on the escapement wheel, but finally discovered what the real issue was - two of the shafts were at the opposite extremes of their positions and this, couple with a slight swash of the gears, resulted in them clashing when they were both in the closest position at the same time - the gearing made this happen every twenty or so hours and the drive to the escapement was blocked. Centralising the shafts seems to have cured it now - all is running well after a day and a half. An odd failure that I've never seen before - it probably occurred because of the way I held it to wind it up before I refitted the face and hands.