Hi Darc
I'm not a specialist of the bloc B but I have several Bloc S and D45s that have all in common this kind of clunch command: none of them are leaking despite the absence of any gasket at this place.
My hypothesis is just that you overfilled the bloc with too much oil : le level shoud be below the level ot this screw.
I hope it helps
Feel free to share a beautiful picture of you bloc B
Oil leak - Bloc B
Re: Oil leak - Bloc B
R55c, C44c, C4c, R33a, moteur V7C 
, D45s, Solex 3800, Peugeot S57 
(ben oui: nul n'est parfait !!!)
, D45s, Solex 3800, Peugeot S57 (ben oui: nul n'est parfait !!!)