Interesting thoughts. I found a manual and it specifies the exact torque for the gearbox type. However you are right, that no mechanic will look up that kind of stuff for every car that comes in.
For your interest, the manual mentions 2 drain plugs which in itself is interesting. I only saw 1 when I looked, and yes on further inspection there are 2. Both needed to be drained.
The manual specifies 40 - 58 Nm for the drain plug on the bottom, and 21 - 31 Nm for the drain plug on the side. Plus 25 - 39 Nm for the fill plug.
I have done the drain and refill now, and I second the idea of making sure you can get the fill bolt off first. I spent about a week off and on trying to get the fill bolt off. It was so tight. Plus it was square, so I couldn't use a normal socket and breaker bar. I eventually used some heat from a small blow torch, and it came off after that.
The drain bolts came off easily. Based on how easy this was I changed the oil in my diff too using limited slip diff oil.