Everyone worries about the water leaking from the outer tube of the riser, at least that gives you a warning to repair/replace. The big big problem comes when water leaks from the outside water jacket into the hot exhaust side before the shower head then ending up in the motor, unfortunately water doesn't compress but connector rods do bend...
There's very hot gas on one side of the pipe and much cooler water on the other side, heat cycles and electrolysis eventually win. If getting new make sure to get them with the hard coat insulation.