Stephen
I have a D365 as well and my bilge is in the same state as Godwin’s above. She’s a 2009 D365 and any boat of that age will get some moisture ingress especially from the pressure relief valve on the calorifier or general condensation, it all eventually collects in the bilge. Mine has the same hole that your pinky fits in, but it’s filled with Silkoflex. I have just got on the boat this evening after 4 weeks away and the amount of water in the bilge would not fill a teaspoon. When we first got the boat 3.5 years ago its bilge was about 1/2 as bad as yours, but i found if its left wet, especially salt water the non-return valve on the bilge pump pipe actually corrodes and leaves you with the staining you are seeing. I have the same non-return valve as the one in your picture and your is in about the same state as mine was. I just spent half a day cleaning it all out, scrubbing off the contamination and greasing the bolts as Godwin has done and there are no leaks from the bolts. I have looked around other D365’s and there bilges are spotless and others are like mine and yours, it generally comes down to how well the previous owner actually looked in the bilge. Some owners of any yachts just periodically turn on the bilge pump, but never actually look in the bilge itself, and if there is a couple of inches of water it corrodes the valve on the end of the pipe. Being an engineer i check mine every single time i get on the boat and every time i leave the boat so i know what state it in. This does not help you make the decision, but not all bilges are spotless. As someone has mentioned above you could use it to negotiate the price down. after you get the boat give it a really good clean and see if you still get water ingress. Remember to clean out the bilge pump filter, mines behind the batteries in the starboard rear cabin. The cover just unscrews and you remove the filter and wash it out.
John