Update:
I fitted the diff yesterday evening, took me about 4 hrs in total including fitting new seals to the diff, they are relatively cheap at €37 for the two and 4 spring clips
New seals are the rubber coated type the old ones were bare steel with a rubber lip.
I knocked them in using the old seals as I had nothing that size as a drift.
My arms are a bit sore today from benchpressing the diff several times in order to refit it.
If you do this, remove the companion flange before attempting to remove or refit the diff, on a manual the pipework for the clutch gets in the way.
Not a big job to take it off there is a 24mm nut lightly staked to the shaft holding it on.
The diff only holds 1.2 litres of 80w-90 so I am going to replace this more often, given that the split is 50/50 front rear the oil is going to be under more pressure than the 2.6l in the rear diff.
Personally I think a lot of the failures will be because of seal failure and oil breakdown.
The input shaft has two taper roller bearings and the front one has more stress on it as the load is off centre when the pinion is driving the ring gear, any wear here will probably make the gear meshing a bit haphazard and could lead to tooth chipping or similar.
My own diff failure was down to not spotting the oil seal failure in time, but given the relatively low oil capacity it can leak away quite quickly before you realise, especially doing motorway speeds.
More frequent diff oil changes would have spotted it before it caused trouble.
Top tip to remove the old seals