I replaced the gearbox oil my manual 2.2. Then went on the do the transfer box and back axle, they are more straight forward.
I cannot recall the gearbox having a level plug. From memory it has a drain on the underside of the gearbox and a refill plug in the top. Its not to bad to get to the filler plug. You remove the under tray and battery, the radio isn't coded. I then undid the bolts in the fuse box and lifted off the top, and flexed the bottom of the fuse box for more access, then remove the bolts from the battery tray and place the tray to one side, then you can access the filler plug on the top of the gearbox. It is awkward but achievable. Don't do what I did and loosen the bolt on the ac pipe on the top of the engine thinking it was a mounting bracket, the pipe is in two halves and you loose gas. I have a manual Draper oil pump which holds 1 litre of oil with a flex pipe and bent metal filler pipe. I removed the metal filler pipe on the end of the flex and pushed the flex into the top of the gear box. I measured the amount of oil removed from the gearbox which was just over 2.3 litres and I put 2.4 litres in. You need to check the correct fill amount as different cars have different amounts of oil in the gearbox. Someone might know the correct fill amount. Hope this helps