Sportage diesel clutch slipping

I didn't even know this model has a dual mass flywheel!  You sound very sure about the diagnosis, but how does this cause such a strange intermittent slippage?  More info would be super-helpful, as I still haven't got the dealer to accept something's wrong, although I know perfectly well that it is!

Thanks again. 

After a series of trials by me and the dealer, including stall tests which would normally expose failing dual mass flywheel OR slipping clutch, there has been no recurrence of my problem over at least the last 400 miles!  The supplying dealer was very good and helpful about it but, understandably, wanted to see the nature of the problem for himself before starting to replace parts which might be in perfect working order when stripped out.

 

Having searched my memory very carefully about all the times my clutch was slipping - and bearing in mind I was always very quick to back off the throttle to avoid making the problem worse - I am beginning to wonder if the problem actually lay with the clutch master cylinder.  This seems hugely unlikely because in effect the pedal acts directly on it, but I can recall a few times sensing that the pedal was not returning fully to its normal rest position as quickly as it should.  Could it conceivably have been a bit of grit or roughness impeding the master cylider's action for a second or two, which has now cleared????  If so, its a new phenomenon for me in over forty years driving!  I'd really rather like it to recur so that I can clear up the mystery, and will report further if it does.

 

Good luck to others with similar symptoms, but I have found out in the last few weeks that both clutch and dual mass flywheel failure on the Sportage are really quite rare in normal driving.