1965 C15F Gear Selector Oil Leak

[Liendrof]

Hi
I have a substantial amount of oil leaking from around the gear selector.
Have read on hear a number of cases of oil leaking from the Kickstarter but none from the gear selector.
The bike has been standing for 2 years.
Any ideas please.

[Liendrof]

Update
After draining off the engine oil and leaving the sump open, the leak has stopped.
I have left the sump off for two days and the oil continues to dribble out.
It appear the due to the bike standing the oil has drained from the oil tank and flooded the sump causing the oil to leak along the gear leaver shaft.
I assume that the dribble out of the sump is oil returning through the drain hole in the gearbox inner cover.