i bet i have done a hundred of those things , the cheap route is to remomve the pipes and lightly grind out the hole and corrosion if its cracked then drill two very small holes , one at each end of the crack to keep from spreading . i used either marine tex $$$ or the slow dry jb weld , i have had none to come back from this method . if you have some money to spend then get them welded but know this , there is still a high chance of a pin hole from a less than perfect weld so be prepared to use a epoxy any way , best just to use jb to start with , i have never replced one b/c of a crack or pin hole unless its on the mounting flange