RV refigerators life span?????????

We had a 1978 Jayco Cardinal pop-up whose fridge was still working when we sold it in 1996. Since 1996, we've owned 3 5th wheels with RV fridges. 2 of them had fridge cooling unit failures at 3 months and 6 months of age respectively - these included both a Norcold and a Dometic. If it matters (and I doubt that it does), the RV fridge that didn't fail was a Norcold.

The current 5th wheel has a residential fridge with inverter for obvious reasons....

Rusty