Leaking stanchions/cleats and leaking deck/hull joint are two separate issues.
The stanchions/cleats leaking is extremely common on Bavaris of this era, but relatively simple to fix by taking the top/back covers off the furniture inside to access the backing plates and nuts. Not the best of access, but sufficient. The stanchions are long levers and will keep on moving, so it's best to use a flexible sealant like butyl. Edge it off on the outside with normal adhesive sealant to avoid the permanently sticky dirt-collecting edge that butyl gives you. The cleats and fairleads don't move so regular sealant is fine.
The deck/hull joint issue on our boat was that Bavaria didn't use enough sealant in there, leaving big gaps, but we have a different toerail from the B37 (teak cap instead of aluminium profile with fairleads). This leak was mostly only noticed when we dip the rail (which we almost never do) or strong wind is forcing rain in. I would fix the toerail fittings first and then see if you still have an issue with leaks. On our boat, I took off the exterior teak rubrail which hides the joint, pulled out the old sealant, cleaned up the joint and injected plenty of new sealant, pushing it in further while fairing with a putty knife. After this, all leaks from this area were gone. It's also not a difficult job, although somewhat time consuming (especially doing it standing in a tender, although this was more convenient than a boatyard scaffold). A few of the rubrail screws were difficult to extract. I assume on the B37 you will need to remove the aluminium rail for this job, which looks like more work.
The spongy wood is only an issue if it is a significant part of it so the rail is at risk of pulling out. It can still be fixed with epoxy injections though.
For the damaged furniture, I can recommend Ronseal wet rot wood hardener to stabilize. Or replace parts as you see fit.
Overall definitely cause for a price reduction depending on the extent of the damage, but if you're willing to take on the work I wouldn't let it put me off the boat. Although letting it progress to the point where the furniture takes damage shows general lack of maintenance and I would cautiously inspect the rest of the boat with that in mind