I had the same problem on my '04 limited. I lubed the exterior linkage in every way possible and it still squeaked. I solved it by removing the inside panel of the rear hatch (one screw under the round cover in the hand grip, and reach under an edge and pop the panel off). You will be able to see the spoiler motor/gear drive assembly. I put a little dab of BMW #10 lubricant, which is kind of like red axle grease, on the gear drive, cycled the spoiler a couple of times and the squeak was gone for good. It took all of 10 minutes to do.

Bob...