We've had issues with few of our games on route, but overall they've been rock solid.
LED lights used to illuminate the backbox on WWE CPU board went dark within a week. Stern replaced the CPU, solved.
Node board fried on KISS when a coil used by one of the pops shorted internally. That's not supposed to kill the board, but it did. Stern replaced the coil and node board, solved.
We've been very happy with Stern's support - Chas is awesome!