If you used the brass plug it must be leaking around the seal. If so, no rust advancement and leak sealer may help you keep driving. If steel was used, could be rust, but 3-4 years? antifreeze and water? May still be the plug seal. Are you sure it's the plug? Not an emergency if you keep watch on water level. Hope you get to feeling better. Getting at that plug may be a big job.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn