My DMF was replaced recently following clutch judder. Its a massive problem with most diesel engines. MAnufacterers fit them to aid smooth gear selection.
The problem is that they are made up of springs and rubber seals, and as they are sealed units they arent servicable.
I got to see my damaged dmf once it had been removed, the recomended amount of play is appprox 10mm, mine was about 40mm.
Luckily it was replaced under warranty, an after market warranty at that.
one other thing is the clutch should be replaced at the same time. FAlse economy for it not to be. I argued this point, but after seeing my old clutch at even 45k it was starting to break up slightly.