Having changed the oil in my gearbox to Castrol Syntrax Universal - 75W/90, which is regarded as the best oil for use in both the gearbox and the differential, I thought I'd post a link to a very useful tool.
I did buy a 3/8 drain plug key too, £3.49 from Halfords. Not technically necessary as you can just use a 3/8 ratchet of course. I did have to use the key, with a 3/8 spanner, though when reinstalling the drain plug as there wasn't quite enough clearance to get the ratchet in!
For anyone else contemplating an oil change here's the order you should probably do things in.
1. Jack and support car at its maximum, safe working height. The more room you have under there the better!
2. Check FILL plug can be removed. Many members have found that theirs have been rounded by previous attempts. You don't want to have drained the oil to then find out you can't refill it!
3. Remove the plate covering the exhaust.
4. Remove drain plug making sure you've got a suitable container underneath. Be prepared it gushes everywhere!
5. Apply sealant to drain plug and refit. I used non setting sealant but perhaps PTFE tape would have been better - quicker and less messy if nothing else!
6. Refill gearbox with 1.06 litres of new oil - I highly recommend the tool above for this.
7. Refit fill plug.
8. Check for leaks.
9. Refit exhaust cover plate.
10. Lower car and check for leaks once more.
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