One issue we come across with cast iron radiators is that between sections a leak can develop. Radiator sections seal in two ways: older radiators will have a tapered push nipple friction fit into the sections and the sections will be held together with a draw rod. In newer (still old) radiators the sections are held together with a threaded nipple and a seal between each section.
Radiators held together with draw rods are susceptible to leaks over time as a result of temperature fluctuations causing expansion and contraction for many years. The nipples themselves are more prone to deteriorate due to the wall thickness. When relocating these radiators mishandling can result in a disruption in the seal between the nipple and the section of the radiator.
Rads with gasketed sections are less susceptible to the nipples rotting due to an increased wall thickness. Leaks in these radiators are almost always a result of the gasket deteriorating.
Steam systems are a lot more prone to getting leaking nipples as a result of the acidity of the condensate from the steam system, and over the course of 100 years, this same acidity concentrate will eat these sections of steel away. Fortunately, most steam systems have chemical treatments designed to combat the acidity of the condensate and scavenge oxygen out of the water to extend the life of the systems. The still remains a viable solution – 120 years later, the system is working and in full operation.