That is probably from bilgewater when you are heeled far to one side. This happens on my E35 on the port side at the intersection of the sole and furniture. If so, it is likely through the wood and replacing the wood is the only way to resolve.
I've noticed the same thing at the bottom of my starboard setee. Not anxious to rip out that panel, though. The wood seems to be solid, but some of the teak veneer has peeled away in a couple of small spots.
I replaced the veneer on mine not knowing the true cause of the problem and now it is returning. Luckily when I replaced the sole I used a separate piece there that I can easily remove. My plan is to once again replace the veneer but also seal the bottom edge of the furniture plywood with epoxy to prevent the water from absorbing.