I am not familiar with the diesel in the WK's but, as said it's burning oil that has gotten into the combustion tract. It can come from bad valve seals or valve guides. I used to have an old Mercedes that would do this and it was caused by a bad diaphragm in the cam driven vacuum pump. I don't know if yours has a vacuum pump, but if it does, this would be another place to look. Mine would start all of a sudden and, just like yours, put out massive amounts of blue smoke, but the vehicle would run fine. Good luck and let us know what you find.
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