Manual transmission OIL leak

Good mornig, I need some advise.
My Patrol is a 2009 CRD with 45.000km and manual transmission.

Everytime I come back from a 4x4 Expedition trip of more than 2-3000km I find some oil leak in the lowest part of the manual transmission box.
Right between the transmission and the transfer case.
The oil seems to come out from the lowest bolt.
But the bolt is tight.
I have also checked the Hole close to it but it seems clean and without any oil inside.

I suspect this happening when I do 4x4 driving in very hot conditions, because it never happens when I daily drive my Car in normal conditions.

Any suggestion or similar experience?