Talking MZs at various rallies,I have heard of two cases of the clutch drum coming loose.One from the bloke it happened to,the other from someone who knew someone.It seems to be fairly rare,and my guess is its cause is incorrect assembly and/or inadequate tightening.
A new clutch inner should solve it,I think it is the pressure plate that you need,the tapered inner is part of it if memory serves,[its been about two years since I last stripped my clutch].Both the MZ shop and Ost2Rad have them at £46 and 40 euros.
Best of luck with it.