Hi Stephen, I have a Dufour 44P since new from 2006 and dealt with a similar issue a few years back, I changed all the bent plates (replacing the thinner ones with new 10mm and re bedded them. You could well be right about the leak coming from a different source so I would ask (assuming boat is on the yard) can you have the most suspect plate checked by removing the nuts and plates and checking the threads. In my case the sealant extended into the threads under the nuts/plates and when I removed the sealant all the bolts were clean and like new. Conclusion was the leak was from elsewhere. We found it in the anchor locker, there is a fault with all dufours here from that era. athe packing/filling between the two skins of the hull falls out around the drain holes and each time the bow dips below the surface, water comes in. we found it was this by taking off the stainless steel plates, using timber bungs and sikaflex to seal the holes and did a sea trial. No ingress so we raked out the holes filled them in completely and re drilled them using finger and epoxy to run a smooth fillet around the hole. This has cured the problem and although my bolts were outwardly rusted like yours, they were clean under the adhesive and with new plates, torqued and re bedded have been fine. Cant comment on the sump hole other than if the is no evidence of seepage from the sealant at the keel/hull joint when the boat is lifted then it may be okay, I would however have the hole mechanically opened up and remade to prevent crevice corrosion in the future. Good luck.
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