[RC-Monster Mike]

Nick's endcap is the only one of its kind out of hundreds of units - I wouldn't worry about experiencing this type of failure with either material as a rule. There is no substantial strength advantage with the steel(advantage is in wear). The aluminum caps are stronger than some steels and are still recommended for most applications at half the weight of the steel caps. In an application with a high side load(diff offset substantially from the center), the steel caps are recommended for improved wear inside the outdrive bore, but otherwise the aluminum caps are optimum.