Last year when I pulled my (2007) boat apart, I discovered cracks in the ends of the crossbars. The cracks were present at all four corners (front & rear, port & starboard). The cracks were very similar to the pictures posted by fastcat, although not quite as bad yet.
I was fortunate in that I had spare front & rear crossbars, so I could still get the boat on the water. I took the broken crossbars to a welder and had the cracks welded and ultimately ended up using my spare front crossbar and the welded rear crossbar (I wanted to use the rear crossbar if possible since it has the newer traveler car system). But when I took the boat apart this fall, the rear crossbar had cracked again at the welds.
Looking at the crossbar, I think there is a flaw because the design of the tramp track causes a stress concentration under torsional load which makes it very difficult for the crossbar to resist torsion without spreading open (the 17 crossbar profile is different than other Hobies and not strong enough to withstand the "hoop stress" generated by the hulls trying to twist relative to one another). This cyclical spreading of the crossbar ultimately causes the crossbar to crack right next to the tramp track. In fact, I mounted a crossbar end casting to a 2 foot length of 2x4, inserted it into the crossbar and twisted and the crossbar spread open pretty easily.
So, the solution I'm going to try will be to add a stainless steel band around the outer edge of each end of the crossbars. It is a 5/8" wide, 0.025" thick band clamp held in place with a 10-32 machine screw. The hope is that that this will will add enough strength to the end of the crossbar to keep it from spreading open and cracking (or continuing to crack). The only issue may be the fit into the hull which could be a little tight due to the extra material, but I did a trial fit with a small section of crossbar and was able to get it installed. I'll update on the results after I put the boat back together this spring.
sm