Hi roddy
There are a few of possibilitys for cause of the leak.
1, Incorrectly tightened drain plug or not sealing due to damaged threads
2, Gear box level incorrect (overfilled) The filler plug is slightly higher than the correct level point (level 5mm below bottom edge of filler hole)
3,Gear box input shaft seal from the clutch. Requires gear box out and casings separated so a new seal can be fitted. can also be caused by over filling
4,Drive shaft seals, which you will need a special ftting tool to obtain correct seal alignment/positioning. Also can be caused by over filling.
5, Drive shaft roll pins loose or missing allowing drive shaft to move away from the ideal sealing point or the roll pin ends not sealed off with silicon sealer.
6, Gear box casing joints, either the paper gasket on the bell housing or the loctite 518 red sealer are failing, both require the casings to be separated.
I know it's a long list but they the most common causes for a leak towards the front of the box.