Well, the problem has been there from the very start, so it's definitely not too late. I've just been continuing to put miles on it since I first identified the problem, about 2 days after picking the car up.
It's been to MMC several times, had all the seals replaced, lining ripped out, and now has a new roof. If you ask me, that's definitely not fit for purpose. I think I've been very understanding with it so far, as Mac says!
Been chatting to one of the field engineers at Lotus who is flying up from Hethel to MMC tomorrow just to look at my car as he thinks he knows what it might be (although why did he not say that when he first looked at it??). You don't get engineers flying up for personal service with a BMW do you?! Although you don't generally get leaking roofs with them!
So, hopefully it'll be sorted tomorrow. But if it's not, I'm definitely pursuing the hand it back option. It's not fit for purpose and they've been trying to fix it for 5 months. I don't see how they can argue otherwise, regardless of the mileage on the car (just about 5000 now, although about 1000 of that is probably trips to and from MMC!!)
D