Hi Michael,
I'm afraid it's a feature of the cars it's even mentioned in the handbook for the Series I (and I think the II), but as I am overseas I can't quote it to you. No doubt a Series I owner can give you chapter and verse.
For the Series II, they altered the way the diff was mounted and allowed some compliance into the system through the use of rubber bushes. Certainly, when I drive my car I do not notice it at all, but it may feel a bit dare I say it 'under-engineered' if you've come from a Porker.
However, for most of us it's just a design feature and part of the indelible character of the car. You'll quickly get used to it, so please don't let it put you off buying a great drive.
Happy Morganeering
Brian
