We have heard of only one instance of cracks in a Brock Long-EZ exhaust system. It occurred at the flange where the pipe is welded to the flange. Careful inspection is necessary to find this type of crack. You may even need to lightly sandblast the area to detect these cracks. After these cracks were welded, there has not been any further sign of a crack but it is being inspected regularly. There are several types of exhausts that are currently being used on EZs.
Our own experience is limited to the exhaust systems made and sold by Ken Brock and to systems we have welded up ourselves. Exhaust systems, even on certified airplanes, are generally on-going maintenance problems. A simple, four separate pipe exhaust system we tried recently has been plagued with cracks. In fact, every time we have taken the cowling off, we have found cracks all the way from minor, little cracks to major cracks, all the way through one tube.
So far, we have severely damaged the prop only once, when a rather large piece went through the prop, but we have been fortunate to catch potential problems before they became serious by careful inspection. Any and all exhaust systems should be removed to be very carefully inspected at least every annual. If you have a history of exhaust system cracks, check it every 50 hours. The most reliable exhaust systems we have used on the VariEze were made by Herb Sanders of Memphis, TN, who sold out to Sport Flight which is now located in Florida. On the Long-EZ, by far the most reliable exhaust system has been the one made by Ken Brock Mfg.