('04 XJ8 w/110K miles, owned since new):
Following a 2 hour hwy trip, I parked the car andreturned an hour later to leave. When I tried to start it, the Message Center said "Gearbox Fault" and it would not start! Several hour later, I tried again and it started right up, but now the Message Center brieflysaid "Restricted Performance". I then drove the car and it ran fine. This has never happened before...what's going on?

 

It's your transmission. The ZF trannies in these cars are, as someone else said, "ticking time bombs". My wife's tranny in her 1998 XJ8 did the same thing. Had to have it rebuilt - cost around $4K.

Good luck....