The Mini Cooper has long been a part of the roadways of Britain where this economy vehicle was first produced by the British Motor Corporation in the late 50s. The 2nd generation Mini Hatch/Hardtop was introduced almost fifty years later in 2006. While folks generally love these vehicles, now owned by BMW and produced from 2007 to 2014, they do experience the occasional mechanical problem.
One issue that has been noticed by Mini Cooper owners is an apparent water leak into the interior of the vehicle. While this problem does not occur every time it rains, it is usually detected after a period of rain and not, as has been noted, after taking the vehicle to a drive-thru car wash. As well, water has been observed dripping from the rearview mirror and onto the dashboard. This did not occur immediately after it had rained, but up to several days after as if water had accumulated somewhere in the car's roof.
One possible entry point for this water could be the seal around the sunroof. While the sunroof was designed to be waterproof, it could be compromised at some point and may be allowing water to collect under the roof that eventually works its way down to the rearview mirror.
Whether the leak is coming from the sunroof or from another access point in the car, water leaking into the interior of your 2nd generation Mini Hatch/Hardtop can only cause further damage in the long run and needs to be addressed. A local Mini Cooper service expert should be able to help you resolve any problems you may be experiencing with water leaks.
Search for a local, independent Mini Cooper repair shop with Mini Cooper mechanics that have dealer-level expertise at a fraction of the expense.