Gearbox oil leaking

[Reddevil01]

I have brought a peugeot boxer 320 symphony campervan. I used it for one weekend to test it out and all was well with the world. Then I decided to give this van a full service. So I done oil, air filter, fuel filter and gearbox oil change. On this van there is no dipstick. So I looked on the net and it says 2.5 liters of oil. So I changed it but since I changed the oil its been leaking in the pics showed. Only leaks on one side. So the question is did I overfill it and thats why its leaking or does it mean I need a new part? I cleaned it all up and within a minute it starts to leak again. You can see from the last pic where the leak is and its just that one side. Anyone has this before?

 

[Reddevil01]

And it also leaks when the rubber gromit /pin thing is in the hole.

 

[gus-lopez]

looks to be the speedo drive?