The bolt may have been repaired, but there may also need to be rubber and/or plastic gaskets and bedding to keep the water from getting in. The sizes and order of the pieces can make a difference. I have a 2” rubber gasket, followed by fender (big, wide) washers, and then nuts on the centerboard of my 5o5 dinghy. Your setup should be even more substantial if you’re dealing with a weighted keel. If you’re getting water above the floorboards after just one day you should be able to see the water coming in, if it’s coming in via the centerboard bolts.