Tools used -
17mm long reach socket
13mm socket (I used a standard one but you may find it easier to use a long reach)
13mm ring spanner
5mm allen key
large vise + two pieces of soft wood
press tool - buy this tool here http://www.totallyalfa.com/index.cfm?fuseaction=admin.dspProductForm&id=138
long tommy bar
Parts fitted -
2 x diff bearings
2 x diff housing seals - fitted to seal holders
2 x seal holder 'o' rings
liquid gasset sealer
For my guide I have assumed you have already have the gearbox out of the car and it is on your woorkbench.
Use the 13mm socket and 5mm allen key to remove both of the seal holders, which are either side of the diff housing. Note which hole the allen headed bolt came from and which seal holder came from which side of the casing - they are different in shape and thickness, This will help you with the re assembly later. Also you may find a shim behind one of the seal holders - keep it safe and make a note of which side it came from.
With the seal holder safey put to one side use the 13mm plus 17mm socket and the 13mm ring spanner to remove the diff cover. With the diff casing off you can now carefully remove the diff an dcrown wheel.
Next tightly clamp the crown wheel in a large vise using two pieces of soft wood to protect the crown wheel from damage. Now remove the crown wheel's fixing bolts using a 17mm socket and a long tommy bar. With the crown wheel removed from the diff you can place the new diff in postion. Replace the fixing bolts, I found traces of studlock when I removed my bolts so when replacing them I cleaned them off and put a drop of stud lock before retightening them.
Next I fitted the new bearing to the new diff. I used a press and a special press tool which I made up to ensure the bearings were not damaged in any way.
With the bearings pushed on as far as they will go it is time to put the diff and crown wheel back in its housing. Carefully place them back in the housing making sure the bearings are all seated correctly.
Then after covering the joint faces with a thin coat of sealer loosely fit the cover so that the diff is held in place. With this done fit new seals into the seal holders, remove the old 'o' rings, fit new ones and again smeer the joint faces with sealer. Now loosely fit the seal holders in place. Remember to fit them the right way around and to fit the shim in place.
Once everything is loosely fitted you can fully tighten everything down. I tighten the seal holders first as they and the shim ensure that the diff and the crown wheel are correctly aligned. When everything is fully tighten up you are ready to slot the gearbox back into your car and enjoy your handy work but remember to fill the gearbox with oil first!