BMW X5 tail and brake light problems

[NebHurr8]

My girlfriend has a 2004 BMW X5 SUV and the tail lights keep burning out. First, it was the right tail brake light (upper white portion) 8 months ago. We replaced the bulb, then it burnt out again on the left side (upper white portion again). My girlfriend took the 2nd burnt out light to the local garage who said something was probably wrong with the socket and then replaced it (verbal account given to me by her). Now only 1 month later, the right tail night lights (middle red portion) are out. First, it was the just part of the right tail light (middle red portion) and 1 week later the whole right tail light (middle and lower red portions) and the brake light (upper white portion) burnt out. Any ideas what to do or how to troubleshoot this problem? My girlfriend is thinking about taking it to the BMW dealership, but I thought I would post here first.