Looking at it recently, the FWD heat exchanger appears to be liquid-to-liquid. The failure mode of that would be clogged/compromised passages or reduced flow through the cooler (bad pump? although you would likely have other problems if that was the case).
I haven't stressed mine at all but it has never come on in the couple hundred miles I've logged. When I bought it, the seller specifically told me he was thinking of just deleting it as there is enough cooling capacity to address the heat load for the duty cycle of a camper. I chose to keep it... I'm not willing to roll those dice, and it was easy enough to relocate.