Gear Box Oil

["Mike Razor" <mrazor@mis.net>]

I know this was discussed but for the sake of brevity, what oil goes
in a 78 MGB with O/D?
The guy at the service station and I read the owner's manual and it
stated to use whatever you put in the engine. I put 20/50 Castrol.
While he has it he is going to clean out the filter and replace the
fluid, but I remember some discussion about what to put in and before
we get started I wanted to make sure.
THANKS!
MIKE R