Possibly unrelated but I guess you're looking for clues, so here goes.
On my 4th (also LSD), the retaining clip that holds the drive shaft into the gearbox was missing on one side. It actually drove okay but when you were underneath you could get the shaft to 'float' in and out a little.
I was having other issues related to shake (CV joints going, a tyre that had been left flat distorting the casing), so I can't really tell whether the missing clip gave any extra shake. I had CV Joints and the retaining clip done at the same time and the shake is no more.
Might be worth a look anyway.
**EDIT** Here's the exploded diagram I had from D2M Tuning and I believe it was the part labeled 7, 23, 24. I'd ask an actual mechanic before you order anything though, I'm just repeating what my spanner-man told me
