This is very shoddy customer service from the BMW dealer. If I had spent the best part of £40,000 on a sports car then I would expect them to investigate. It reads like the windscreen wipers have become warped - this is common on cars that have been left outside in the hot weather for a long period of time with the wiper blade becoming curved and skipping over the glass. The wiper blades will need to be removed and twisted back into shape or replaced.

If the dealer refuses to take this issue seriously, make a complaint to the service manager. Juddering wiper blades are a minor issue, but present serious safety challenges if they are not working as they should. The BMW dealer should really address this.