No symptoms, no warnings. I only discovered the problem during recent snow. Ironically parking on a slope in a local winter sports shop trying to buy a steigh for my grandkids. I could not reverse up the slope with forward wheels spinning. I checked prop shaft and it turned.
I got my local Indie to fit mine as not so young anymore. He charged me £250. However. There are a lot of instructions and youtube videos on this repair but not a job for me!
http://forums.swedespeed.com/showthread.php?t=467785
Again, good luck.