Hi, just driving home and turned into my road fairly quick in second gear, there was a bit of a jolting then it started to make a crunching sound.
Put it into third to get it to my drive.

Now its realy hard to get into 1st, put it in 2nd and lift the clutch out and it does nothing, 3rd 4th 5th and reverse are fine at the minute, does this sound like second has given up on me?

 

could be selector fork broken,
see - http://www.gears.tv/products.html#subaru

 

How easy is it to replace the centre diff?

Does it just bolt off and back on?

 

Centre diff comes off quite easy. Took my box off the other day. See me post jammed in 1st. when u get gearbox off just undo the bolts, not the very back ones where the prop goes but the next lot further along. You will see as you look from the side the different section. Go easy and prise it off and mine stopped i had to lift the gear selector rod slightly to get it out of the selector forks then it just slipped right off... you will need a new gasket tho when you put it back...

But doing it while the gearbox is still on the car, not so sure... can foresee lots of cuts on hands and bumps on head!