Mine also broke and I agree with the bad design idea.
WHen I reordered them through Isuzu they sent one of a different design that seems like it would be a little less inclined to seperate like that.

When mine broke the first time I slipped it back on, made sure the 4 "nipples" went through the 4 holes, heated it slightly with a torch and hit the nipples with a hammer to get them to flatten out a little. It worked for well for a while after that, too. Although looking at the pics you've only got two nipples left <img src="/forums/images/graemlins/smile.gif" alt="" />