DEAR MISS MANNERS: It happened AGAIN last week for the umpteenth time: I took my car in for maintenance at the dealership, which prides itself on customer service. I waited in the very comfortable lounge while the work was completed, paid the invoice, walked out and got into a sparkling-clean car that had just been washed as part of the service. I had driven less than a block when I realized that the seat was out of adjustment. At the first corner, I looked in the exterior rearview mirror, only to find that the mirror had been knocked out of its cradle and was giving me a view of blue sky. Whe…