Steve
Below is extract from the email that I received from the Technical manager of Penrite
"The friction characteristics do differ for each fluid. BMV is a DEX3 type of fluid but uses a slightly modified chemistry package to enable the ideal gear shifts to occur in ZF 4 and 5 speed boxes (especially the latter)"
I changed the gearbox oil simply by draining and refilling. I know that this will only give about 50% synthetic but I figure that next time I service the box I'll repeat the process and that should take me up to 75%. Can't say that I've noticed any difference in the changes as the box was always very smooth. I'm just chasing the increased operating temperature ability of the synthetic as I tow a heavy caravan.
Russell

