I'm pretty sure that as there is an absence of a mast compression post that the load is taken up by a ring beam spread through the coach roof to the hull. The bulkhead between the saloon and the V berth for'd is certainly not load bearing and a bukhead only exists on the starboard side. The portside is open access to the V berth. The keel case is simarly not load bearing. I am hoping that Dehler will respond to my email request for construction details. I can find no previously reported problems of this nature with this model. The boat is a Van de Stadt design and this guy was no mug. I am beginning to think that it is water ingress into the wood immediately below the mast via the screw holes that hold the tabernackle to the coach roof, probably marine ply but I am unsure just how intricate the replacement will be if it is a ring beam and the integrity of the structure is to be preserved. From previous research I learned that these boats were built to sail in the Baltic and considered to be sturdily and well constructed, just got unlucky I guess.
The forestay is not adjustable but the backstay is. Thanks for your suggestions so far, Ian