Caulier Brewery whose website announces (warns?): "from a time long ago fallen into oblivion". It also shows a couple of differently branded beers. I'm wondering from that if I've got an old label of the beer. I cannot find "Bon Secours" on the brewery site at all. Is "Caulier Brune" the relabelled beer?
In any case, the one I've got pours very dark indeed, which is a good sign. The first aroma is a bit turpentine, though not completely unpleasant. The taste is very sharp, acidic wood stain initially and in the aftertaste, but in between the two there are some other flavours: burnt malt, roasted almonds and coffee. It's much like a cold ristretto with alcohol (8%).
It's interesting, it's certainly complex, and it does mellow out a bit over time. Still, that acid aftertaste doesn't seem to evolve. I'm not sure I'd go too far out of my way to this one again.