I had one snap on my vitesse last year at about 35mph,heard a bang and saw a wheel disappearing across the fields and then realised it was mine then the car went for a womble and managed to beach it on the grass verge ,luckily there was no kerb.Like yours mine showed it had been cracked for awhile.Have to see if my new one from Taiwan lasts any longer?
I can remember my mates herald doing the same on the A23 coming back from Brighton in the dark back in the 70,s,went back in the morning to recover the car,never found the wheel though!
When I used to race/rally cars always made sure I didn,t swap shafts from one side to the other.
martin