Gearbox Oil change interval

[Gandi69]

What milage are people dropping their gearbox oil at?
Or are these boxes sealed for life units like the PSA/Rover r65 (of which Ive done a few changed on even though they are supposedly never require a change according an friendly rover engineer I know)

 

[Gray]

they are not sealed units iirc.

I personally do mine once a year, every 12K ~

 

[Gandi69]

Any special tools required? Ive got some square ended gearbox drain plug adapters that fit into half inch drive.

My spelling is truly atrocious today so apologies