2018 Subaru Outback - melting mirror cover Mystery

[SFY]

I have 2018 Subaru Outback. Same problem with melting mirror covers. 90% time parked in garage. Contacted dealer, they replaced exterior mirror covers and within 3 days had melted again. No rain. They even put silicone at seams to prevent water seeping in. Passenger side worse. They have checked electrical systems. They have opened a technical ticket. They called to inquire about external heat sources in garage. There are no heaters in the garage. I've had this car since new Nov 2017. I see many posts relative to this issue. Why after 70 months would this happen all of the sudden and then happen again within 3 days? My dealer is great. The service manager is great. I love my Subi. I see this same issue posted on Lexsus, Subaru and others forums from 2015 forward. I have to wonder if it is only on autos with certain manufacturer of plastic body parts or those with electric exterior mirrors. It is a mystery.

 

[Esteban]

Heated mirror malfunction I would think.