Just plan on replacing it on any boat you my buy. Simple; old = replace. not a matter of if but when. The tank on my boat went when we were planning a trip to the bay last year. only took 2 days to remove the the old out and new in. Any metal tank will have sludge in the bottom unless you get really lucky and find a boat that someone already replaced the tank in. If your buying old boat it's kind of silly to not think your tank/s will leak eventually. (imho)