jmf

Solved: the top of the thing seen in the picture can be taken off, there are 5 hex screws. It is actually a thin metal plate having an o-ring underneath. Applied silicone under the o-ring, put it back, screwed the plate on top and voila, no m0ar leak. I guess the plate had somehow deformed because the impression by the o-ring was clear on the top of the plate (on the inside) but not so much on the bottom, hence the leak.