On the last leg of the journey, 20km from home, we are cruising at 100 kmh.
Suddenly, loud noise and vibration.
I pull over gently, expecting to find a punctured rear tyre, but they're all inflated.
Slid under the van and grabbed the prop shaft. Oh dear, it's quite wobbly.
Seems that the rear bearing of the gearbox has disintegrated.
Thankfully, it was all fairly level to slight downhill except for the last half km, so I nursed it along at 40 kmh with the hazard lights on.
In the morning, I'll take to it with some spanners, and we'll see what the extent of damage is.
Bad luck Mike. Don't forget to take a 14lb sledge hammer with you (the Persuader!) should it look too grim. It won't do the car any good but it may make you feel a whole lot better 
