You have a repeatable condition not resolved by BMW. If I was your mom I would be checking into lemoning the car. Your case I would be bringing the entire repeatable problem to the BMW service manager and ask what help they can provide.
If that doesn't get you some help I would contact BMWNA and explain the situation and state the problem still exists.
Failing that I would get a lawyer and take them to small claims court to be perfectly honest.
I say this because you got a car they never fixed from day one unless I don't understand what you posted. That repeatable problem unresolved is a problem not a clean the seals and you are good to go solution.
Sounds harsh but most of us have zero issues with our convertibles. Those that do seem to never get the problem resolved. BMW needs to step up to the plate and get these leaks corrected. It will not happen until you play hardball with them and if you go to small claims court and get satisfaction I would get rid of the car...