Noticed it today. A small raised line between two of the blocks IYSWIM. Not wide - I'd struggle to get a fingernail tip in it - but I'm petrified it's going to get worse.
Is in the area next to the drainer, but there are bits that get miles more water and it hasn't happened there. Have sinking feeling is the vile Milton solution from DS2's steriliser.
I have added coats of oil religiously as per care instructions.
Please tell me all is not lost, give any tips to stop it getting worse and if by any chance you know of a good drainer/dishrack with a bottom, for wooden worktops, I will love you forever... 