My RX-1 heat exchanger cracked at 6-7000 miles or 10000-11000 kilometers on the left side rear skid mounting bolt. I don't believe it's the flexing of the running board that causes this, I think it's caused by the flexing of the funnel and skid that makes this happen. By looking at the position and direction of the crack my conclusion is that when the tunnel flexes the pressure around the mounting bolt rises and over time the heat exchanger encounters metal fatigue and cracks.
The exchanger can be welded by a TIG (maybe other methods as well) but it will have to be sinked into an acid bath for cleaning before welding. My local welder didn't have the acid bath at the time he tried to fix mine, and a cause of that he was not able to stop the leakage, it was better than before but not a permanent fix.