Another Forum Member had a "wipers continuing to run" problem (along with other issues) and it apparently turned out to be an electronics module.
See this post for "dd123"s problem and the recommendations as how to handle it with the dealership.
Wiper Problem
You just have to document every occurrence and be persistent about insisting that your dealer actually finds the fix for the problem instead of just trying to brush you off. Often the dealership does not have the expertise to find and correct complex problems and is reluctant to contact BMW NA or BMW AG and ask for help. If you feel they are not giving your issue the attention it deserves, you should let them know that you are going to phone or write BMW NA and ask them to intervene.