Exact same thing happened to me..
My solution was to replace the pieces of galvanized pipes with longer ones that went all the way up into the cap. This involved cutting to length and drilling a hole through each end - one for the hinge pin on the bottom, and one where the rivet goes that holds the cap in place. I wasn't able to rivet the new version, so I used a screw post: http://www.hardwareelf.com/elf/fasteners.jsp Lowes has them.
Was this more work than I really wanted to do? Absolutely, but I'd already got a deal on another pair, and I didn't want them breaking again. Plus, poorly designed stuff just pisses me off. All they need to do is use pipes a couple inches longer, and problem solved. Since then, I've had no troubles, and I regularly carry between 4-6 boats on them. Word of caution, if you use a chop saw or bench grinder like I did, do it in a very well ventilated area. Galvanized metal gives off some really harmful fumes when it's heated.