Just had my 6000 mile service done here in the UK for the grand sum of £87 (about $174). Quite reasonable I thought and nothing abnormal with the bike.
At the same time I also mentioned that my panniers were loose with as much as half an inch of "play" in the top mounting. The solution, dealer has ordered complete new pannier backs! I thought there were some "shims" that could be used, but they know best
BMW does make some special rubber shims for this. The kit consists of three pairs of different thickness I am not sure what message board it was on, but it was within the past month. Search here or on the I-BMW board.
This is a $6 part in Canada. I don't think new case backs will fix the problem. So as nice as that is, save yourself some time and aggravation. These are self-installable easily. 2 minutes and I had done both my cases.