Mini Cooper Rear Brakes

Measure them yourself? You can pick up a special brake thickness tool for $6. But most experienced techs guess at the thickness.

By the sounds of it, you have break pad life left to use. You may have some pads worn down to 2mm in a spot, but I bet the dealer is saying there is 4mm left, and measuring the thicker part of the pad if worn unevenly. Never the less, you have pad left to use. Although 4mm and 2mm especially, really is not that much pad. But if the dealer won't go good until worn down some more, so take it in towards the end of the service contract, the pads aut to be worn down by then. But also listen for metal on metal noise or the wear clip noise, take it in at that time to be looked at.