Our Safe-T-Alert 35 Series (35-742) CO/Propane detector in our 2012 FF 214WSD is at end of life (beeping/lights). Before ordering an exact replacement I see they have a newer model Series 85 that is smaller but coves with a trim piece to fit the 35 Series hole. The customer service person at MTI, the manufacturer wasn't able to explain the difference in models or the exact dimensions. Anyone have experience with the 85 Series? Thank you!