Thanks for replies.

It's a standard FRS box so supposedly has quaife diff and the inside of it certainly looks the same as the one I had for my IB5 box. The clattering sort of noise is only when you bring the clutch up. Otherwise the box is nice and smooth and silent whilst I gear.

I bought the box second hand off flee bay, and was told it had done 51k. No idea though. I obviously put fresh oil in and even let it run out to start with to try to give it a little flush. The bit of old oil in there didn't look that bad and certainly wasn't swirly or black. Quite normal in fact.

There is a chance it's an inner cv but does seem there is more play in the box than usual, only in my experience.

Thanks again!