Front diff might suffer from the same disease as any others, i.e. the planetary gears wear into the cage causing lots of metal in the oil as you describe. I haven't had this on mine but did on my Series 1 Discovery and the diffs are identical. The diff was dismantled because radar-ears detected a slight gear noise when cornering and the gears were so spaced out due to the wear that it was just starting to chip the tips off the gear teeth, another few hundred miles and it would have gone bang. I was quite chuffed because everybody told me I was hearing things
No apparent rhyme nor reason as to which ones do it and which ones don't, I suppose I have seen about a dozen like that in the last ten years, some 110s and some Discoverys. Older diffs (so I am told anyway) had a fibre washer between the gears and the cage to stop this, newer ones don't. If you take the front diff out the problem will be immediately obvious if you look at the cage, on my one the side gears (the ones the halfshafts go through) were worn about 5-6mm into the cage on both sides! Eventually what happens is that the teeth strip on the planetary gears and you get no drive through the diff.
No known turbo problems according to the info I have, and I can't recall a single Td5 turbo fail here. Can't say I have ever stuck me finger up one though... not sure what "normal" play is supposed to be.