Our Jazz has now been repaired by our local main dealer (who have been superb by the way), It was collected yesterday am. and returned early evening all courtesy of Honda.
If my understanding is correct, the repair required the removal of the gearbox, clutch and flywheel - a lot of work, and was apparently required to cure a leaking plug in the the engine casing. The reason this blanking plug exists does not seem obvious to me but it is supposed to be sealed by a crush-washer and this was apparently leaking oil presumably into the clutch/bell-housing. I may be wrong but I think this could be mistaken for a leaking crank-shaft oil seal in that oil would I imagine drip out of the bell-housing drain hole. I was told that a new main bearing oil seal was fitted during the repair and so that should be one less thing to worry about in future.
I asked if we had been very unlucky as the Jazz has such a good reputation for reliability but was told that, no the dealer had rectified quite a few of these.
I am pleased at the way this has turned out, the fault was spotted during the second service and the Honda dealer made great efforts to fix it with the minimum of trouble to me - very reassuring!