Although stainless steel as used in keel bolts, is a wonderful material, be aware that there is a situation where it will let you down. The situation that you need to be aware of is when stainless steel remains immersed in stagnant seawater. In such situation stainless steel will corrode, and resulted in me having to change one of the keel bolts in a previous boat. Where you have evidence of rust around the keel to hull joint, you need to ensure that it is not the keel bolts that are decomposing. If the seal in that area begins to breakdown, it is most likely that the exposed area of cast iron keel is rusting and hence the weeping rust stains seen. Do nothing about it and any seawater trapped and remaining stagnant in that area will then result in corrosion of the stainless keel bolts.
The same problem can occur in the exhaust system where a stainless silencer is fitted and where the boat is rarely used. Look at the first splash of water to come out of the exhaust when starting the engine. If its brown then corrosion is probably in progress. If the stainless parts become holed you will notice water entering the bilge along with carbon monoxide gas into the enclosed area of the cabins. Be warned !!
Best of luck in dealing with the problem.