Here's the longer version of events, make up your own opinions as to what is to blame.

The old diff:
- back lash galore
- leaking

When I installed the stiffened mount it raised up the end of the box about an inch or so, that mount surprised me with how saggy it was straight out of the packet. First drive and only noticed the lightest whining ect. Along comes the weekend and a come & try day at the local track and I enter it. Two corners in and I remember how crap the rear end of this car is, it's lifting the inside wheel like a dweeb. Two laps in on a sweeper and I hear the worst noise I could possibly imagine in 3\4, there was a harsh scratching and a massive grinding whine. The scratching was some bolts scratching the tail shaft, cut excess off the bolts and running another tail shaft thought I suspect it is probably fine. The Sunny shaft in it is sitting 1\2 way on the yoke, and doesn't have an oil splash hat, the box does have the big version on its output seal.

I managed to drive it home (albeit slowly) and put it up on the stands to investigate. I 4th gear the rear end was quite visibly twisting with any application of torque. I can't actually get the gearbox drain plug off to inspect the oil for shavings (I swear they used a whole bottle of loctite or something!!, I've tried a blowtorch to try and break the bond). The diff oil did have shavings, and quite a lot of metal dust to boot. So given those circumstances I pull out the diff, clean out the shavings and throw in a slightly less crap center.

Upon inspecting the original center I could only find signs of harsh wear on the crown and pinion, the bearings (couldn't see the pinion bearing) appeared fine.

Anyway come this morning and a long sweeper corner brings back the harsh whine in 3rd\4th, I have driven it far more sedately since.

Would running a shorter shock keep those angles in check?