Leigh, we did solve the issue on mine. We changed both the boot seal and then the middle brake light unit. I think it was mainly (or possibly only) the brake light unit. But that did not stop the wiper motor, we just had water in boot after rain.
Back in 2015 I did have an issue when the alarm started to intermittently sound and also, I think, the rear wiper motor had stopped. That turned out to be caused by water from the wiper motor unit. On my A3 the washer fluid goes through this unit and had started to leak, dropping down I guess to an alarm sensor. The answer was a replacement wiper unit (I also bought a wiper arm puller).
Hope that helps.
PS Was away Friday/Saturday and did not check email, otherwise would reply earlier. Good luck.